- Unauthorized Activities: The Chinese research vessel Tan Suo 3 was accused by the Philippine Coast Guard of conducting illegal scientific research in the country’s Exclusive Economic Zone (EEZ) without proper authorization.
- Geopolitical Tensions: The incident has heightened tensions in the South China Sea, a region already marked by territorial disputes between China and several Southeast Asian nations, particularly the Philippines.
- Diplomatic Response: Manila has lodged a formal protest and reiterated the importance of respecting international maritime laws, especially the 1982 UN Convention on the Law of the Sea (UNCLOS), which defines EEZ rights.
A fresh maritime dispute has erupted in Philippine waters, with the Philippine Coast Guard (PCG) accusing the Chinese research vessel Tan Suo 3 of conducting unauthorized marine scientific research within the country’s Exclusive Economic Zone (EEZ). The incident, which took place approximately 92 nautical miles off the coast of Burgos in Ilocos Norte province, has reignited tensions between Manila and Beijing in a region already fraught with territorial disputes in the South China Sea.
The Incident Off Ilocos Norte
According to the PCG, the Tan Suo 3 was first spotted within the Philippine EEZ on May 1, 2025. On May 5, an image captured by the Coast Guard showed the vessel retrieving a manned deep-sea submersible identified as Shenhai Yongshi (Deep Sea Warrior), capable of diving to depths of up to 4,500 meters. The PCG also documented the recovery of a yellow underwater drone by a rigid hull inflatable boat, raising further suspicions about the nature of the activities.
PCG spokesperson for the West Philippine Sea, Commodore Jay Tarriela, stated that the Chinese vessel’s irregular movements were “inconsistent with freedom of navigation” and indicative of marine scientific research, which violates the Philippines’ sovereign rights. “They were instructed to cease their unlawful activities, clarify their intentions, and ensure continuous transit within the EEZ in compliance with both international and Philippine laws,” Tarriela added.
The Philippines’ Response
To counter the presence of the Tan Suo 3, the PCG deployed the BRP Teresa Magbanua (MRRV-9701) and an aircraft to monitor, challenge, and potentially escort the Chinese vessel out of the EEZ. The PCG emphasized that such actions demonstrate their effective presence in preventing unauthorized activities in Philippine waters, sending a clear signal of Manila’s determination to defend its maritime sovereignty.
The Chinese Embassy in Manila has not yet issued a response to the allegations, but this incident is the latest in a series of events that have heightened tensions between the two nations.
A Context of Rising Tensions
The South China Sea has long been a geopolitical flashpoint, with China claiming vast swathes of the sea based on its so-called “nine-dash line,” a demarcation that overlaps with the EEZs of several Southeast Asian nations, including the Philippines. In 2016, an international tribunal in The Hague ruled China’s claims invalid, a decision Beijing has refused to acknowledge. Since then, the Philippines has ramped up efforts to monitor and counter Chinese activities in its waters, often with support from international allies such as the United States.
This is not the first incident involving Chinese devices in Philippine waters. In January 2025, a yellow underwater drone, suspected to be of Chinese origin, was discovered off the province of Masbate in central Philippines. Local analysts suggest the device may have been used for seabed mapping, an activity that could serve military or strategic purposes.
Chinese Technology Under Scrutiny
The Shenhai Yongshi, also known as Deep Sea Warrior, is a state-of-the-art manned submersible developed by China for deep-sea exploration. According to official sources, the submersible was designed to conduct scientific missions at extreme depths and is equipped with advanced technologies, including buoyancy materials, lithium batteries, and mechanical arms, almost entirely produced domestically. In 2018, the Shenhai Yongshi was scheduled to undertake 50 missions in the South China Sea and the southwestern Indian Ocean, some of which were for archaeological purposes.
However, the use of such technologies in foreign waters without permission is considered a violation of international law, particularly the United Nations Convention on the Law of the Sea (UNCLOS), which grants coastal states exclusive rights to conduct marine scientific research in their EEZ.
Regional Implications
The incident has sparked concerns among neighboring countries. International commentators have suggested that the Philippines, alongside Taiwan and Vietnam, may need to unite to counter China’s expansionism in the region. “If you don’t show your strength, China will soon come to your lands and conduct investigations there as well,” warned one social media user, echoing a sentiment shared by many in the region.
Meanwhile, some observers fear that China may have broader intentions, such as constructing artificial islands for military purposes or appropriating natural resources, as it has done in other parts of the South China Sea.
An Uncertain Future
The episode off Ilocos Norte marks yet another chapter in the strained relations between the Philippines and China. As Manila continues to bolster its maritime presence and seek support from the international community, the challenge remains to balance the defense of its sovereign rights with maintaining regional stability. With China showing little intention of backing down from its activities, the South China Sea remains one of the world’s most contested and potentially volatile regions.
