One of the potential flashpoints in Northeast Asia is the maritime territory disputed between the People’s Republic of China (PRC) and the Republic of Korea (ROK) in the Yellow Sea. In 2025, the situation escalated into a standoff between the coast guard vessels of the two nations.
What is the PMZ and the Background to the issue?
In 2018 and 2024, China installed two semi-submersible buoys in the PMZ. In 2022, a fixed steel structure was built, believed to be a repurposed decommissioned oil rig. Subsequently, China set up several more large steel structures (two in April and May 2024 and another in early 2025), having made the ROK apprehensive for several reasons, despite China’s insistence that these structures are intended for aquaculture.
First, the ROK claims that the steel structures installed by China could impede the passage of South Korean fishing vessels.
Second, South Korea fears that China is applying “grey-zone” tactics to expand its maritime sovereignty, similar to the construction of artificial islands carried out by Beijing in the South China Sea, where small installations were transformed into artificial islands hosting radar systems and military airstrips. The concern is that China will first build the structures, and then, under the UN Convention on the Law of the Sea, unlawfully claim maritime sovereignty based on their presence, basically turning disputed maritime areas into de facto Chinese territory.
Third, the narrative of a Chinese threat is periodically blown up by representatives of the United States. For instance, on 9 December 2025, Victor Cha, President of the Department of Geopolitics and Foreign Policy and Chair of the Korea Chair at the Center for Strategic and International Studies (CSIS), called on the United States to flag China’s installation of maritime structures in and around the jointly managed zone between South Korea and China in the Yellow Sea as yet another example of Beijing’s tactics towards America’s regional partners.
Cha noted that what the new US National Security Strategy prescribes for the South China Sea is applicable to the efforts of South Korea and the US to maintain freedom of navigation in the Yellow Sea: “Resolute measures must be developed alongside the deterrence necessary to keep these lanes open, free of ‘tolls,’ and not subject to arbitrary closure by one country.”
Conservative media in South Korea consistently point out that “China’s actions threaten not only Korea’s maritime sovereignty but also the fragile balance of regional security in Northeast Asia” and that “South Korea should step up efforts to prevent China from possibly carrying out strategic operations to expand its control in the West Sea (Yellow Sea),” calling for a proportionate response.
The Chinese Ministry of Foreign Affairs acknowledges that China and South Korea have overlapping maritime claims and that both sides are advancing negotiations on the delimitation of the sea space. However, according to the Ministry, the fish farms established by Chinese companies in the aforementioned waters do not violate the corresponding agreements between China and South Korea.
Developments in 2025
On 26 February 2025, a two-hour standoff broke out between coast guard vessels of China and South Korea after Chinese authorities put paid to Seoul’s attempt to investigate a steel structure in their overlapping waters of the Yellow Sea. In the wake of this Chinese move, the ROK Ministry of Foreign Affairs summoned a representative from the Chinese embassy to lodge a protest.
The incident began with South Korean authorities having dispatched the research vessel Onnuri to the PMZ to inspect a steel structure that China had installed without permission. As the vessel approached within about one kilometre of the structure, Chinese coast guard ships and three rubber boats carrying civilians hindered the South Korean vessel from attaching research equipment to the structure. The Chinese side stated that the structure was an aquaculture farm and requested the Korean vessel to leave.
On 25 March, the Democratic Party (DP) expressed “strong regret” over China’s installation of yet another steel structure and asked China to immediately cease construction of any facilities that could “undermine the trust” established between the two countries, and to cooperate with Seoul’s investigation.
On 26 March, Minister of Oceans and Fisheries Kang Do-hyung announced that, as a countermeasure, South Korea had installed a “large fixed floating structure” in the PMZ “to initiate an environmental investigation in the area.”
On 31 March, to protest against the structures, the Korea Veterans Association arranged a rally near the Chinese embassy in central Seoul, stating that “China’s unauthorised installation of large-scale steel structures is a direct challenge to our maritime security.”
At a meeting of officials in April 2025, the parties failed to resolve their disagreements. The South Korean side demanded that China relocate the disputed structures outside the PMZ, warned that it would consider taking “proportionate countermeasures” if this demand was not met, and articulated “absolute intolerance” for any additional structures. The Chinese side cited difficulties in complying with such demands and proposed organising an on-site inspection instead.
On 31 May, ROK officials stated that China had installed three more large-scale buoys near waters adjacent to South Korea, bringing the total number of such Chinese floating installations in the country’s waters to 13.
On 24 September, the vessel Onnuri entered the PMZ. Approximately six hours later, it was approached by a Chinese Coast Guard vessel and two other Chinese ships. A South Korean Coast Guard ship also headed to the area to provide possible support. The Korean vessel was reportedly “caught in a pincer movement” by the Chinese ships. They subsequently tracked the movements of the South Korean research vessel and the coast guard ship for about 15 hours, approaching to a minimum distance of 3 kilometres.
In October, Democratic Party lawmaker Lee Byung-jin made public recent shots of the Chinese installation, which depicted people, including some in diving suits. He found this unusual and alleged that the structures in the West Sea could be part of China’s long-term strategy to strengthen its de facto control over disputed maritime areas, akin to the country’s expansion in the South China Sea, with potential military implications.
Is the Problem Being Resolved?
According to President Yoon Suk Yeol, he brought up the issue in his conversations with the Chinese President, including during their most recent meeting in Beijing in January 2026, where they discussed the maritime matter. Subsequently, China reportedly began to take action. It was reported that the Chinese had started removing one of the disputed steel structures, a move that South Korea on 27 January 2026 described as “significant progress” that would contribute to the development of bilateral ties.
Chinese Foreign Ministry Spokesperson Guo Jiakun also stated at a briefing that a Chinese company was working on the removal of a fish farm management platform, referring to it as an independent operation conducted under the company’s guidance in accordance with its management and development needs.
On 4 February, Chinese Ambassador Dai Bing stated that there was progress in dismantling the disputed steel structures built in the overlapping waters of the Yellow Sea. However, the politicisation of the issue and the influence of the United States will clearly hinder it from being resolved in the short term.
Konstantin Asmolov, PhD in History, Leading Research Fellow at the Centre for Korean Studies, Institute of China and Contemporary Asia, Russian Academy of Sciences
