Continued Korea-China Standoffs in the PMZ

By Jennifer Jun, Asia Maritime Transparency Initiative, and Victor Cha

Left: Image of the Shen Lan 1, the first of the two aquaculture cages to be deployed inside the South Korea-China Provisional Measures Zone (PMZ), tethered to a support vessel. Right : View of the Shen Lan 2, May 30, 2025. Copyright © 2025 Vantor. Image may not be republished without permission. Please contact [email protected].

Key Findings

• In late September, Automatic Identification System (AIS) data from Starboard Maritime Intelligence shows that a South Korean research vessel and its coast guard escort entered the South Korea-China Provisional Measures Zone (PMZ) and approached one of China's aquaculture platforms, prompting a standoff with the Chinese coast guard.
• Multiple China Coast Guard vessels tailed the Korean ships for over 15 hours, at times as close as 1.7 nautical miles, before the Korean vessels withdrew from the zone.
• The incident echoes a similar high-profile confrontation in February 2025 and is part of a broader pattern of Chinese presence operations around unilaterally deployed structures in contested waters.
• According to the South Korean National Assembly, China has interfered in 27 out of 135 South Korean maritime surveys since 2020; roughly one in five.
• The South Korean Navy has also confirmed the deployment of at least 13 unmanned, lighthouse-shaped Chinese ocean observation buoys in the Yellow Sea between 2018 and 2023, raising concerns about their potential dual-use nature and long-term strategic implications.
• China's use of its coast guard to patrol the perimeter of the PMZ and shadow Korean government and research vessels in the area resembles grey zone tactics that Beijing has employed in the South and East China Seas to assert control over disputed areas.

Report

In late September, tensions between South Korea and China regarding the Provisional Measures Zone (PMZ) in the Yellow Sea (Sohae) once again flared. According to Automatic Identification System (AIS) data from Starboard Maritime Intelligence, South Korean research vessel Onnuri entered the South Korea-China PMZ in the Yellow Sea on September 24. Approximately six hours after the Onnuri entered the PMZ, the China Coast Guard (CCG) 6307 patrol ship maneuvered to follow it, and two additional CCG vessels were dispatched to the area from port in Qingdao. At the same time, the Korea Coast Guard (KCG) 3009 approached the area to support the Onnuri. On September 25 the Korean vessels approached the Shen Lan 1 and Shen Lan 2, Chinese aquaculture installations which the South Koreans contest due to lack of prior consultation before their deployment in the jointly managed zone As the Onnuri neared the Chinese platforms for likely observation, as it has done in the past, it was flanked by two CCG vessels.

After passing near the Chinese platforms, the Onnuri and the KCG 3009 were each trailed by two CCG vessels for the next 15 hours as they headed back east. The CCG only ceased shadowing the Korean vessels once they had left the PMZ: the KCG 3009 exited the PMZ at 21:00 UTC on September 25, followed by the Onnuri six hours later at 3:00 UTC.

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[SLIDESHOW] Automatic Identification System (AIS) data visualizing the September 2024 encounter in the South Korea-China Provisional Measures Zone (PMZ). South Korea's research vessel Onnuri and KCG 3009 are shown approaching Chinese aquaculture cages before being closely tailed by multiple Chinese Coast Guard vessels. The overlapping trajectories illustrate close proximity and prolonged shadowing.

This encounter mirrors the standoffs that occurred earlier this year such as the February 2025 episode, which received widespread media and public attention in Korea. However, this latest incident highlights the ongoing pattern of deliberate presence and surveillance near China's unilaterally deployed platforms in contested waters.

According to a recent KBS report citing a South Korean National Assembly member's office, South Korea conducted 135 maritime surveys between 2020 and the present, with Chinese interference reported in 27 of them, roughly one in five. For example, in May, the Chinese coast guard disrupted a South Korean vessel observing whales.[1] Yang Hee-chul, the Director of the Ocean Law and Policy Research Center at the Korea Institute of Ocean Science & Technology (KIOST), believes that Chinese actions in this disputed maritime zone are designed to declaratively demonstrate its intention and ability to assert primary rights over these waters.[2]

In addition, recent analysis by South Korea's Navy confirmed that China has installed at least 13 unmanned, lighthouse-shaped ocean observation buoys across the Yellow Sea between 2018 and 2023.[3] While civilian in function as ocean observation buoys, their deployment in sensitive areas and near maritime boundaries also raises questions about long-term strategic utility. The South Korean Ministry of Foreign Affairs acknowledged and expressed concern for potential dual-use of the buoys and said that it is monitoring the situation closely.[4] These concerns have been further amplified by a photograph recently released by a South Korean member of the National Assembly, which showed at least three individuals on Shen Lan 2, with one wearing a dividing suit and appearing to conduct maintenance on an oxygen tank. These sightings raised additional concerns in South Korea about the platform's functions and non-civilian use.[5]

The 2001 South Korea-China Fisheries Agreement, which established the PMZ to help manage overlapping exclusive economic zone (EEZ) claims, focuses on traditional commercial fishing activity and does not clearly authorize or prohibit the deployment of aquaculture structures or observation buoys. Efforts by China to restrict the navigation of South Korean vessels in the PMZ, however, would clearly violate the United Nations Convention on the Law of the Sea (UNCLOS), which grants freedom of navigation to all foreign vessels within the EEZ. While China's use of its coast guard to patrol the perimeter of the PMZ and carefully shadow Korean government and research vessels in the area does not technically violate the terms of the agreement or of UNCLOS, it resembles grey zone tactics that Beijing has employed in the South and East China Seas to use overwhelming and persistent coast guard presence to assert control over disputed areas.

[1] Yang Hyeon-seung (양현승). "중국, 서해 해양조사 상습 방해…5번 중 1번 '어깃장' [China Routinely Obstructs Ocean Research in the West Sea-1 in 5 Missions Thwarted]." KBS News, September 25, 2025. https://news.kbs.co.kr/news/pc/view/view.do?ncd=8375032.

[2] Ibid.

[3] Report by the Republic of Korea Navy submitted to the National Assembly, shared with the press.

[4] Lee Keun-pyung, Lee Yu-jung, and Park Hyun-ju. "Lighthouse-shaped and solar-powered: Photos reveal China's 13 buoys in Yellow Sea." Korea JoongAng Daily, June 3, 2025. https://koreajoongangdaily.joins.com/news/2025-06-03/national/defense/Lighthouseshaped-and-solarpowered-Photos-reveal-Chinas-13-buoys-in-Yellow-Sea/2321658.

[5] Jin, Hyesook. "'잠수복 입은 수상한 인력…중국 서해 불법구조물 군사적 활용'" [Suspicious Personnel in Wetsuits… Chinese Illegal Structures in the West Sea Used for Military Purposes]. Yonhap News Agency, October 22, 2025. https://www.yna.co.kr/view/AKR20251022133100704?input=1195m.