It is the second time the countries' coast guards have held training drills together, following their first joint maritime exercise in the Philippines in 2023.

Friday's simulation of a collision, fire and person overboard, which AFP reporters will observe, cap a week of exercises off Japan's southwest coast that began Monday.

Dozens of personnel are taking part in the drills that officials say are not targeted at any one nation -- while using language often employed by Washington and its allies to indirectly refer to China.

Hiroaki Odachi, the regional head of Japan's coast guard, said the exercises aimed to contribute "to the realisation of a free and open" Asia-Pacific region.

Tensions between China and other claimants to parts of the East and South China Seas have driven Japan to deepen ties with the Philippines and the United States in recent years.

In 2024, the three countries issued a joint statement that included stronger language towards Beijing.

"We express our serious concerns about the People's Republic of China's (PRC) dangerous and aggressive behavior in the South China Sea," it said, describing "dangerous and coercive use of Coast Guard and maritime militia vessels".

They also expressed "strong opposition to any attempts by the PRC to unilaterally change the status quo by force or coercion in the East China Sea".

- 'Volatile flashpoint' -

China and the Philippines have engaged in months of confrontations in the contested South China Sea, which Beijing claims almost entirely, despite an international ruling that the assertion has no legal basis.

Chinese and Japanese patrol vessels in the East China Sea also routinely stage face-offs around disputed islands.

Friday marks the 214th straight day that Chinese vessels have been spotted sailing near the Tokyo-administered disputed islets known as the Diaoyu in China and Senkaku in Japan, according to the Japan Coast Guard.

The current record is 215 straight days in 2023-24.

"Such persistent intrusion raises a risk of accidental collision or confrontation in the East China Sea," Daisuke Kawai, director of the University of Tokyo's economic security and policy innovation programme, told AFP.

Meanwhile "the South China Sea is now regarded as one of the world's most volatile flashpoints, I would say, where any accident at sea could escalate into the border crisis."

"A trilateral coast guard framework bolsters maritime domain awareness and law enforcement capacity, making it harder for any one nation, China, to pick off a smaller player in isolation," Kawai said.

The three countries have also carried out joint military exercises to bolster regional cooperation.

Last week Tokyo and Beijing traded barbs over close encounters between their military planes over the Pacific high seas.

Japan says recent Chinese military activities in the Pacific -- where Beijing's two operating aircraft carriers were sighted simultaneously for the first time -- reveal its intent to improve operational capacity in remote areas.