New satellite imagery has revealed for the first time a hulking steel rig in the Yellow Sea between China and South Korea that has inflamed tensions between the two nations.
The photographs, supplied exclusively to Newsweek, show the latest of several large steel platforms that China has installed in the Provisional Measures Zone (PMZ), a jointly managed stretch of the Yellow Sea, known in Korea as the West Sea, where the Chinese and South Korean exclusive economic zones (EEZs) overlap.
Newsweek reached out to the Chinese Embassy in Seoul and the South Korean Embassy in Washington with emailed requests for comment.
Rising Tensions
An EEZ extends 200 nautical miles (230 miles) from the coast, granting claimant states sole access to its underwater natural resources, including fishing grounds, according to international maritime law.
The PMZ, established under a 2000 agreement, permits only fishing-related activities and navigation in the disputed area until a formal maritime boundary is agreed upon. South Korea, a U.S. treaty ally, says the structure—installed without its knowledge or consent—is viewed by Seoul as violating that agreement.
Unlike earlier platforms reportedly deployed and later removed following protests from Seoul last year, China is doubling down on the presence of its latest jackup rig, named for three long legs that can be lowered to the sea floor for stabilization.
"This issue is highly likely to be a perennial source of contention between the two countries," said Dong Gyu-lee, a research fellow at Seoul-based think tank the Asan Institute for Policy Studies.
Researchers told Newsweek that the pointed placement was likely part of a broader Chinese territorial push, similar to the Beijing's expansive moves in the South China Sea.
Aquaculture vs. Appropriation
The rig arrived in the area in October 2022, according to a review of satellite photos by Ray Powell, director of the Stanford University-affiliated maritime analysis initiative SeaLight. Powell said it replaced a smaller rig that had been sent out at least two years prior. The newer structure is fixed about 115 miles southeast of the Chinese port city of Qingdao.
Imagery captured by Austin-based SkyFi showed the three rig legs anchoring the massive structure to the floor of the Yellow Sea, estimated to be about 160 feet deep. SeaLight estimates the rig measures about 350 by 265 feet, and South Korean intelligence has estimated it towers about 160 feet over the ocean's surface.
Also visible is a helipad, several lifeboats and a platform that could be used to service China's "smart" deep-sea farming cages, such as the nearby Shen Lan 2 Hao, or Deep Blue No. 2, which has also been in position since 2022, Powell told Newsweek.
China's state broadcaster CCTV previously described a similar "offshore fish farm"—sold to Norway for salmon aquaculture—as a "mega-structure."
Powell said the Chinese government could be using the rig in a "salami-slicing" strategy to incrementally expand its presence in the PMZ. "[South Korea] may suspect there is more happening there than just aquaculture, such as signals intelligence operations," he said.
"A classic [People's Republic of China] gray-zone aggression clothed in a perfectly plausible civilian justification," Powell said, echoing a concern previously raised by South Korean officials.
Gray-zone warfare refer to coercive actions that deliberately stop short of direct conflict.
Yellow Sea Face-Off
SeaLight analysts discovered the rig after South Korean media reported a previously unknown maritime confrontation between the Chinese and South Korean coast guards.
On February 25, the Korea Institute of Ocean Science and Technology, a Busan-based private oceanography research organization, sent the vessel Onnuri to investigate the structure. The Korea coast guard deployed the ship KCG1502 as an escort.
The investigating vessels encountered three Chinese coast guard vessels, whose movements became increasingly confrontational as their South Korean counterparts neared their destination at about 2:30 p.m. February 26, according to media accounts.
The Chinese ships performed up-close blocking maneuvers, including on multiple occasions cutting across the bows of the South Korean ships, according to automatic identification system data gathered by SeaLight tech advisory group director Anna van Amerongen.
During the two-hour standoff, China also deployed rigid inflatable boats carrying plain-clothes Chinese nationals armed with knives, South Korean media reported, citing diplomatic sources.
"We have also delivered our firm position to China regarding the reported incident," South Korean Foreign Ministry spokesperson Lee Jae-woong told reporters last month.
Powell used Starboard Maritime Intelligence ship-tracking software to trace the Onnuri's movements through its AIS signature, a broadcast of its location designed to avert collisions, in line with maritime regulations.
"That was when I knew I could find the coordinates of the mysterious 'steel structure' I kept reading about, by tracking that ship's movements on that date," he said.
China's Seoul embassy pushed back against the media reports. It said the facilities were part of lawful deep-sea aquaculture operations in waters off the Chinese coast. The situation in the Yellow Sea was stable and the two countries maintained effective lines of communication on maritime issues, it said.
South Korea and China are preparing for working-level talks on their maritime dispute later this month, according to the Yonhap news agency, citing diplomatic sources.
Meanwhile, South Korea has deployed its own large floating structure in the PMZ as a countermeasure, Minister of Oceans and Fisheries Kang Do-hyung told lawmakers on March 26. He said this platform was being used to carry out an "environmental investigation."
'Strategic Intent'
China is "testing Seoul's resolve," Jun Kajee, a lecturer at Southern Utah University and a research fellow at the Korea Institute for Maritime Strategy, told Newsweek.
The dispute has intensified during a time of political upheaval in South Korea, Jun noted, with the impeachment, ousting and ultimate removal from office this month of former President Yoon Suk-yeol.
South Korea stands at a crossroads as it prepares for a June snap election to choose who will lead the nation as it navigates relations with China—its nuclear-armed neighbor and top trading partner—and the United States, its key ally, as President Donald Trump's tariffs and statements sow uncertainty across the region.
"China has not allowed a good crisis to go to waste," Jun said. "Beijing insists these are private-sector projects for economic development, dismissing sovereignty concerns as overreactions.
"However, China's refusal to halt construction—even as South Korean survey vessels face coast guard blockades—reveals a strategic intent to normalize its presence."
Still, the politicization could cut both ways, Dong Gyu-lee of the Asan Institute for Policy Studies told Newsweek.
"Given the deep political divisions in South Korea, it's not inconceivable that some politicians may spotlight this issue to stoke anti-China sentiment—both leading up to and following the presidential election," he said.
Update 4/17/25, 2:16 p.m. ET: This article has been updated with additional information about the rig's presence and with additional analysis.
Update 4/18/25, 2 p.m. ET: This article has been updated with additional information and comment from Dong Gyu-Lee.