By Ha Er-rui | 2025-12-30

China has steadily expanded its activities in the Yellow Sea areas where the Exclusive Economic Zones (EEZs) of it and South Korea overlap, the Center for Strategic and International Studies (CSIS), a Washington-based think tank, said in a new report. Beijing is using "gray-zone" tactics to widen its influence and erode South Korea's maritime sovereignty, CSIS contends.

A December report by CSIS's Beyond Parallel project said that since 2018, China has installed 13 marine observation buoys "in and adjacent to" the Provisional Measures Zone (PMZ) within the overlapping EEZs. The deployments violate Sino-South Korean rules that prohibit fixed structures in the PMZ and have raised concerns in Seoul, the report says. China has refused to remove the buoys.

South Korea and China established the PMZ under a 2001 bilateral agreement to temporarily defuse disputes over their overlapping EEZs in the Yellow Sea. Recent Chinese activities in the zone have renewed tensions, says CSIS.

South Korea's military publicly disclosed the locations and images of the buoys for the first time in June, saying the deployments showed China was pursuing a strategy of gradual encroachment. China asserts the buoys are solely for meteorological observation, but South Korea's Foreign Ministry has questioned whether some newer buoys may carry military reconnaissance functions.

Potential spying

Several buoys have solar panels, enabling long-term autonomous operation, CSIS said. While their military use cannot be confirmed, their locations suggest an effort to enhance maritime surveillance and strengthen control over the area, it added.

In May, China unilaterally declared several temporary no-sail zones within the PMZ to accommodate drills for its new aircraft carrier, the Fujian. The move aroused a backlash in South Korea, with some commentators telling the Korea Times that Beijing may be accelerating its actions in the Yellow Sea amid political instability in Seoul.

The maritime facilities serve scientific or economic purposes, China says. Beyond Parallel, however, said the buoys could improve maritime domain awareness and be used to consolidate control over disputed waters. The report noted that, compared with China's actions at Scarborough Shoal in the South China Sea, its Yellow Sea operations have been lower-profile, possibly to avoid escalating tensions with South Korea.

"China's actions have clearly violated its agreements with South Korea," Victor Cha, lead author of the report and chair of CSIS's Korea program, told Chosun Ilbo. Seoul has been cautious because of its sensitive relationship with Beijing, he said, adding that "no one wants to see a future in which China claims sovereignty over the Yellow Sea."

South Korea should publicly disclose the precise coordinates of the buoys to allow satellite analysis, said Cha. He urged coordination with the United States, Japan and the Philippines to issue joint condemnations and press Beijing for negotiations.

A threat to South Korean security

China's construction activities in the Yellow Sea threaten South Korea's strategic buffer and western maritime access, the Korea Times said in an October 26 editorial. The area lies close to US Forces Korea facilities in Pyeongtaek. "Korea cannot allow its maritime sovereignty to erode by degrees," the newspaper said.

In November, Chosun Ilbo quoted Stephen Yates, a senior research fellow at the Heritage Foundation, as saying China's tactics in the Yellow Sea resemble its push of the "nine-dash line" in the South China Sea. Inaction by Seoul could turn the West Sea into "a second South China Sea," he said.

The nine-dash line is what China puts on maps to lay claim to more than 80% of the South China Sea.

Separately, South Korean President Lee Jae Myung on December 23 ordered tougher measures against illegal Chinese fishing in the Yellow Sea, citing increasingly aggressive Chinese resistance to enforcement.

At a Ministry of Ocean and Fisheries briefing, Lee said some Chinese vessels use obstructive tactics to dodge inspections. He urged authorities to "make every effort to detain them."

Lee questioned whether current penalties deter repeat offenders, advised raising sanctions to a level that "makes violations unprofitable" and told the coast guard to seize vessels in serious cases.

Meanwhile, South Korea's Foreign Ministry is planning a visit to China by Lee in 2026. Yonhap News Agency reported in early December that Lee told international media he would work to repair South Korea-China relations, while exploring security cooperation to ensure stability in Northeast Asia.