Chinese Platforms in the Yellow Sea’s South Korea-China PMZ

In late February 2025, South Korean research vessel Onnuri made its way to the Provisional Measures Zone (PMZ) shared between South Korea and China. The vessel was deployed to survey one of three Chinese steel structures that were installed in the PMZ without prior notice to South Korea. The vessel’s journey was unsuccessful, as the Chinese coast guard blocked the ship, claiming that the structure was an aquafarm.

Since then, South Korea has requested the three structures be relocated to outside the PMZ, raising concerns that they violate South Korea’s “legitimate and lawful maritime rights” and could “physically obstruct the navigation of South Korean fishing vessels and naval ships.” However, China has rejected the request, repeating that the structures do not violate any agreements, and that “…the relevant facilities set up by China are deep-sea fishery aquaculture facilities located in China’s coastal waters, which are China’s reasonable use of offshore marine resources.” South Korea has responded by taking “reciprocal measure with a large-scale floating object” for environmental surveying purposes.

In May 2025, tensions escalated further when China declared multiple temporary no-sail zones within the PMZ to conduct exercises of the Fujian, China’s most-advanced aircraft carrier, in a move “Seoul views as part of a gradual push to assert de facto control over the region.” Additionally, recent South Korean media reports have revealed that China has installed at least 13 additional lighthouse-shaped, solar-powered buoys across the Yellow Sea between 2018 and 2023, further raising concerns about the expansion of semi-permanent maritime infrastructure throughout contested waters.

Such activities in proximity to South Korea’s designated maritime zones have raised new concerns over China’s intentions and the possibility of a creeping jurisdictional presence under the guise of civilian or fishing activity, consistent with broader patterns of Chinese gray zone tactics observed elsewhere in the region.

Read the full report at Beyond Parallel:

Chinese Platforms in the Yellow Sea’s South Korea-China PMZ

Report’s Key Findings

Three Chinese maritime structures—one integrated management platform [pictured above] and two aquaculture cages—have been deployed inside the South Korea-China Provisional Measures Zone (PMZ) without prior consultation with the South Korean government.
Satellite imagery analysis reveals that one Chinese structure is a repurposed offshore oil platform that serves as a central operations hub for the surrounding cages, with six operational floors and the potential for expanded functionality beyond aquaculture.
South Korean requests for China to relocate the structures outside of the PMZ have not only been repeatedly rejected, but the Chinese government has also unilaterally declared “no-sail” zones within the PMZ and has deployed at least 13 additional buoys in the Yellow Sea since 2018.
In late February 2025, a South Korean research vessel’s effort to survey the Chinese structures installed within the PMZ was blocked by the Chinese coast guard. AIS data analysis also shows that the South Korean vessels have made multiple approaches to the Chinese platforms between 2022 and 2024, often accompanied by South Korean coast guard escorts, indicating years of persistent observation and concern.
While available information suggests that the platforms are genuinely focused on aquaculture, concerns that the platforms may be dual-use for purposes of advancing China’s creeping jurisdictional presence are not unfounded, given China’s track record in the South China Sea, where what were originally weather stations later developed into major military outposts.
Beyond Parallel and Asia Maritime Transparency Initiative commercial satellite imagery and automatic identification system (AIS) data analysis provide the first comprehensive timeline of the development, deployment, and current status of the publicly known Chinese steel structures in the PMZ.