The Chinese military has announced a live-fire exercise in an area in the Gulf of Tonkin from Monday to Thursday this week, warning ships not to enter the zone.
The warning came as Vietnam issued a formal map defining the baseline to demarcate its territory in the gulf. Though neither side linked their action to that of the other, it was unlikely to be a coincidence, some observers said.
China’s exercise comes amid the latest wrangle between the neighbors over Vietnam’s island building in the Spratly archipelago in the South China Sea.
A baseline under the U.N. Convention on the Law of the Sea, or UNCLOS, is the line that runs along the coast of a country, from which the extent of the territorial sea and other maritime zones is measured.
In March 2024 China released its baseline in the northern part of the Gulf of Tonkin, deemed by analysts as “excessive.” Radio Free Asia was the first media outlet to report in April 2024 that Vietnam was considering its own baseline amid concern that China may seek to expand its maritime zones.
The Chinese baseline at some points encroaches about 50 nautical miles (93 kilometers) into international waters, according to analysts.
The U.S. military, which promotes freedom of navigation across the world, criticized China’s baseline, saying it may provide a pretext for China to “unlawfully impede navigational rights and freedoms guaranteed to all nations, including transit passage through the Hainan Strait.”
Chinese drills not ‘a pure coincidence’
“The establishment of the baseline in the Gulf of Tonkin aims to uphold Vietnam’s rights and obligations,” the Vietnamese foreign ministry said in a statement, “It provides a robust legal basis for safeguarding and exercising Vietnam’s sovereignty, sovereign rights and jurisdiction.”
China has yet to comment on its neighbor’s announcement but some Vietnam watchers said China’s live-fire drills appeared to be a response to Vietnam’s baseline.
“Although the exercise area off northwest Hainan island is relatively far from Vietnam’s waters, the timing seems too close to be a pure coincidence,” said Song Phan, a maritime researcher.
The new baseline that runs along Vietnam’s coast “conforms strictly to UNCLOS unlike the Chinese baseline,” he said.
Hanoi and Beijing in 2000 signed a Delimitation Agreement to demarcate their shares of the gulf from the mainland of Vietnam and China in the North to the mouth of the gulf in the South.
The two countries, however, have yet to renegotiate a joint fishery cooperation agreement in the Gulf of Tonkin after the old one expired in 2020.
Edited by Mike Firn.