남중국해에서 필리핀 수산청 선박을 타고 지낸 열흘이 보여준 ‘9단선’의 실체

The nine-dash line is a somewhat enigmatic construct. It extends along the outer limits of the South China Sea, just off the coasts of Vietnam, Malaysia, Brunei, and the Philippines—yet its precise location remains indeterminate. Over time, it has both lost and gained individual dashes.

The then eleven-dash line was created in 1947 by one China (the Republic) and is now being vigorously defended by another China (the People’s Republic). Beijing insists on the inclusion of this line on all maps produced within China, and it sometimes also appears on maps and globes manufactured in China but sold abroad.

What Beijing precisely claims within the nine-dash line is likewise ambiguous. While it clearly asserts sovereignty over all maritime features within the line, the line also encompasses extensive areas of sea in which no such features exist. This raises the question of how Beijing characterizes the waters within the line: does it regard them as territorial sea? Are they considered part of the contiguous zone or the exclusive economic zone (EEZ)? Furthermore, does the PRC recognize the right of other States to freedom of navigation within these waters?

China has articulated its claim in submissions to relevant United Nations bodies, as well as in official position papers. Details may vary but it generally goes like this: China has sovereignty over Nanhai Zhudao (the South China Sea islands), consisting of Dongsha Qundao (the Pratas islands), Xisha Qundao (the Paracel islands), Zhongsha Qundao (Macclesfield Bank and Scarborough Shoal), and Nansha Qundao (the Spratly islands); China has internal waters, territorial sea and contiguous zone based on Nanhai Zhudao, China has exclusive economic zone and continental shelf based on Nanhai Zhudao; China has historic rights in the South China Sea.

This, however, does not resolve the question of where the baselines lie from which China would measure these maritime zones. Nor does it clarify whether China intends to generate such zones from artificially created islands on low-tide elevations (e.g. Subi Reef / Zhubi Jiao and Mischief Reef / Meiji Jiao), or from rocks (e.g. Fiery Cross Reef / Yongshu Jiao), which under the law of the sea do not generate entitlements to maritime zones, or only to a territorial sea.

To begin addressing this question, one may examine the conduct of official organs of the People’s Republic of China in the waters within the nine-dash line, in particular the People’s Liberation Army Navy (PLAN) and the China Coast Guard (CCG).

The Philippines fisheries Agency’s mission in October 2025

The author of this article had the opportunity to observe Chinese conduct in the West Philippine Sea – as Manila calls the South China Sea – during a ten-day mission of the Philippines’ Bureau of Fisheries and Aquatic Resources (BFAR). Between 7 and 16 October 2025, he sailed aboard the BRP Datu Pagbuaya (MMOV-3003), a 30-meter multi-mission offshore patrol vessel. The vessel had a crew of approximately 20, including additional personnel from the Philippines Coast Guard (PCG). The author was permitted to move freely throughout the vessel at all times, including on the bridge, and to speak with anyone on board. The only restriction was the protection of the crew’s privacy, specifically by not publishing their names and by not showing their full faces in photographs.

At certain moments, there were short blackout periods, for example during at-sea resupply operations for Filipino fishermen. Each blackout period was lifted within less than 24 hours following a debriefing with the spokesperson for the West Philippine Sea. These debriefings were conducted via satellite. No photographs or texts were required to be submitted for clearance prior to publication.

The mission included a total of six BFAR vessels, all of the same class as the Datu Pagbuaya. These vessels are built in the Philippines and have a cruising speed of approximately 8.5 knots. The October mission, aimed at supporting local fishermen at sea, departed from a BFAR base in Orion on the western side of Manila Bay and covered Scarborough Shoal (referred to in the Philippines as Bajo de Masinloc, or BdM), Northeast Cay (Parola), Thitu Island (Pag-asa), and Sabina Shoal (Escoda).

Almost as soon as the vessels departed Philippine territorial waters, the BFAR flotilla was shadowed by the CCG. Although the exact coordinates of the nine-dash line remain undefined, in practice it appears to correspond roughly to the outer limits of other littoral States’ contiguous zones.

The size of the BFAR mission’s “escort” varied. From the bridge of the BRP Datu Pagbuaya, at least two CCG vessels were visible at any given time. These numbers increased significantly at various points during the voyage.

Three incidents were particularly insightful:

1. On 12 October, a CCG vessel used water cannons against three BFAR vessels and rammed the BRP Datu Pagbuaya near Thitu Island.
2. On 8 October, a large contingent of CCG, PLAN, and Chinese maritime militia vessels shadowed and intimidated the BFAR vessels as they provided fuel and food supplies to Filipino fishermen off Scarborough Shoal.
3. On 10 October, a China Coast Guard patrol vessel deliberately proceeded on a head-on collision course with the BRP Datu Pagbuaya in waters far removed from any contested maritime feature.

These incidents are presented not in chronological order, but rather according to their distance from any land features. This approach facilitates an assessment of whether China relies on the zonal regime established under UNCLOS as a basis for its actions in the South China Sea.

1. Ramming and water–cannoning less than 3 nautical miles off a Filipino island

The incident on Sunday, 12 October, was reported by Philippine media as well as internationally by outlets such as the news agency Reuters.

Shortly after 08:00, the BRP Datu Pagbuaya departed from the harbor of Thitu Island, the largest feature under Philippine control in the South China Sea. She was accompanied by her sister ships, BRP Datu Sanday and BRP Datu Bankaw. Their mission was to conduct an environmental assessment of the Sandy Cays. These four sandbanks (referred to in the Philippines as the Pag-asa Cays and in China as Tiexian Jiao) are located approximately 2 to 6 nautical miles to the west of Thitu.

These sandbanks had been a flashpoint in the preceding months. In April 2025, China Coast Guard personnel landed on one of the sandbanks and unfurled a national flag. A few days later, the Philippines carried out a similar action.

On 12 October, the BFAR vessels had barely cleared the shallow harbor entrance of Thitu Island when Chinese maritime militia and CCG vessels began to obstruct their passage. According to data released by the Philippines Coast Guard, a total of 23 Chinese vessels were involved—4 CCG, 18 maritime militia, and 1 PLAN vessel. The frigate remained in the background but launched a helicopter from its flight deck, which hovered over two of the cays.

The Chinese maritime militia and CCG vessels appeared to operate in close coordination. Several of them employed water cannons against the BFAR vessels, which sustained some impacts despite evasive maneuvers. At approximately 09:20, the CCG vessel with the hull number 21559 pursued the BRP Datu Pagbuaya. After positioning itself off the port quarter of the Philippine vessel with a slight overlap, it turned to starboard, deliberately ramming its bow into the stern of the much slower Philippine vessel. The BFAR vessel sustained damage to the railing and to a ventilation shaft on the port quarter; however, it remained structurally sound. Following the incident, all three Philippine vessels abandoned their mission to survey the Sandy Cays and withdrew to Thitu Island.

The conduct observed indicates that China does not recognize the Philippine territorial sea around Thitu, as the Sandy Cays lie clearly within this maritime zone. This position stems from the fact that China does not recognize Manila’s claim to Thitu—or to any other feature within the nine-dash line. The closest feature occupied by China is Subi Reef, located approximately 12 nautical miles to the southwest of Thitu. In clear weather conditions, radar domes and other structures constructed by China on Subi Reef are visible from Thitu with the aid of powerful binoculars installed there.

Prior to China’s land reclamation activities, which added nearly four square kilometers approximately ten years ago, Subi Reef was, according to the Maritime Transparency Initiative (AMTI) of the Center for Strategic and International Studies, a low-tide elevation. Under the law of the sea, land reclamation does not alter the legal status of a maritime feature. Consequently, Subi Reef does not generate any entitlement to maritime zones.

2. China Coast Guard intimidation 35 nautical miles off Scarborough Shoal

On the first full day of the mission (8 October), the six BFAR vessels arrived in the vicinity of Scarborough Shoal (referred to in the Philippines as Bajo de Masinloc or Panacot Shoal, and in China as Huangyan Dao). Their task was to distribute fuel and food to Filipino fishermen, most of whom originate from Masinloc on Luzon, approximately 120 nautical miles east of the shoal.

Scarborough Shoal is a traditional fishing ground for Filipino fishermen and lies within the Philippines’ EEZ. China has exercised control over Scarborough Shoal since 2012. In recent years, access to the shoal appears to have become increasingly restricted for Filipino fishermen. One of the fishermen who refueled from the BRP Datu Pagbuaya on 8 October informed the author that they are typically required to remain at a distance of 10 to 20 nautical miles from the shoal; otherwise, they would be driven away by the CCG.

The reduced access has a dual impact on the fishermen. First, their catch is diminished, as the most productive fishing grounds are located at the edge of the reef. Second, their small wooden vessels are unable to seek shelter within the lagoon during storms. Consequently, they must return to port whenever adverse weather is forecast, rendering fishing activities largely uneconomical. To enable continued fishing operations at Scarborough Shoal, the Philippine government provides fishermen with free fuel at sea through BFAR. For the government in Manila, the presence of its nationals is an important element in supporting its claim to the shoal.

On 8 October, the BFAR vessels arrived at daybreak at a pre-determined rendezvous point approximately 35 nautical miles east of Scarborough Shoal. Upon arrival, they received a stern warning over the radio: the PLAN declared a live-fire exercise zone, precisely in the area where the resupply operation was intended to take place. The Philippine vessels subsequently relocated the resupply area. From approximately 10:00 to 16:30, the six BFAR vessels supplied diesel and food to around 50 Filipino fishing boats.

The Chinese authorities did not intervene directly. However, they staged an impressive show of force: the author counted seven CCG vessels shadowing the Philippine resupply mission. According to a tally by the PCG, an additional ten Chinese maritime militia vessels were present. The Chinese deployment appeared clearly intended to intimidate the Filipinos, who were effectively surrounded. The presence of two PCG vessels, which had joined the BFAR mission overnight, did little to alter the pronounced imbalance of power. Even the 97-meter-long BRP Teresa Magbanua, one of the largest vessels available to the PCG, was small in comparison to many of the Chinese units. The PLAN, however, remained in the background.

According to the captain of the BRP Datu Pagbuaya, recent experience suggests that Chinese vessels tend to harass BFAR and PCG units if they approach within approximately 30 nautical miles of Scarborough Shoal. This distance indicates that China is operating according to categories that do not correspond to the maritime zones established under the United Nations Convention on the Law of the Sea. According to the AMTI, Scarborough Shoal is classified as a rock. As such, it generates an entitlement only to a 12-nautical-mile territorial sea. Regardless of whether Scarborough Shoal is considered Chinese or Philippine territory, waters located 35 nautical miles to the southeast of the shoal fall within the Philippines’ exclusive economic zone, as the coast of Luzon lies well within 200 nautical miles.

3. Simulated head-on collision on the high seas

The third incident may be the most revealing in terms of how China conducts itself in the waters within the nine-dash line. This event took place on the afternoon of 10 October. After rounding Scarborough Shoal counter-clockwise to the north—while consistently maintaining a distance of at least 35 nautical miles—the BFAR vessels proceeded on a direct course toward Northeast Cay (referred to in the Philippines as Parola Island and in China as Beizi Dao), where a small Philippine contingent is stationed.

Northeast Cay lies approximately 290 nautical miles to the southwest of Scarborough Shoal. At the BRP Datu Pagbuaya’s cruising speed of about 8.5 knots, this corresponds to a voyage of roughly 35 hours. On the afternoon of 10 October, the vessel was trailing several nautical miles behind the other BFAR units, as it is slightly slower than the rest of the flotilla.

Suddenly, at approximately 15:30, a CCG vessel appeared at the 12 o’clock position, heading directly toward the BRP Datu Pagbuaya. On AIS, the vessel identified itself as China Coast Guard 21559 (MMSI 413875624). The skipper of the BRP Datu Pagbuaya inquired via VHF radio channel 16 as to the intentions of the Chinese vessel; no response was received, and the CCG vessel continued on a collision course.

A few moments later, the Filipino crew called upon the Chinese vessel to comply with applicable collision regulations in order to avoid an incident. Only then did China Coast Guard 21559 alter its course slightly to starboard, passing the BRP Datu Pagbuaya port-to-port with a separation distance of approximately 30 to 50 meters. Immediately after passing, the CCG vessel executed a sharp 180-degree turn to port and overtook the BRP Datu Pagbuaya at high speed on its starboard side.

Visibility remained good throughout the encounter, and the Philippine vessel maintained a steady course and speed. It appeared evident that the conduct of China Coast Guard 21559 was intentional. Notably, this was the same vessel that rammed the BRP Datu Pagbuaya off Thitu two days later (see above).

At 15:33, immediately following the incident, the author recorded the position 11°55.8529’N, 114°46.9567’E using the positioning system on the bridge of the BRP Datu Pagbuaya. There is no land feature controlled by China in the vicinity. The distance to the closest Chinese outpost, Subi Reef, is approximately 70 to 75 nautical miles.

The actions of China Coast Guard 21559 on the afternoon of 10 October therefore constituted a dangerous and most likely deliberate maneuver on the high seas. It represented a further instance of Chinese intimidation directed against a Philippine vessel.

Conclusion

The observations made by the author during the BFAR mission in October 2025 do not constitute a comprehensive study of the conduct of CCG, PLAN, and Chinese maritime militia vessels in the waters within the nine-dash line. They reflect only the events of a single mission conducted by one of the claimant States, namely the Philippines. It would be valuable to obtain detailed eyewitness accounts from aboard official vessels of Vietnam, Malaysia, and Brunei during their encounters with CCG, PLAN, and Chinese maritime militia vessels in the South China Sea. Based on publicly available information regarding such encounters, China appears to act less aggressively toward these States. The reasons for this difference in behavior could be the subject of further study.

Nevertheless, the three incidents discussed provide certain insights: it appears clear that China does not base the conduct of its vessels on the principles of the United Nations Convention on the Law of the Sea. Rather, its actions suggest an approach grounded in power-based assertions. It is therefore unlikely that a clear answer will be forthcoming as to how Beijing characterizes the waters within the nine-dash line.