The United States, India and Japan are set to kick off week-long war games in the Pacific, beefing up naval ties as they warily eye an increasingly assertive China and its military buildup.

Warships from the three countries are to begin the joint exercises on Friday, after an official opening ceremony at the Sasebo Naval Base in southern Japan on Thursday.

Known as the Malabar Exercise, the annual event usually involves India and the US, but Japan's Maritime Self-Defence Force (MSDF) will take part this year, the third time since 2007.

The exercises off Japan's southern coast come on the back of rising regional tensions as Delhi and Tokyo remain embroiled in territorial spats with Beijing.

China is also at loggerheads with some Southeast Asian nations over its claim to large swathes of the South China Sea.

Washington has been increasingly turning its focus to Asia as it looks to counter Beijing's growing influence and a military buildup that has unnerved some of its regional neighbours.

"India, Japan and the United States have a shared strategic interest," said international relations expert Takehiko Yamamoto, professor emeritus at Tokyo's Waseda University.

"The aim of this naval exercise is for (the three countries) to manage a vast sea area stretching from the western Pacific to the Indian Ocean.

"They need to make sure the lines of communication stay robust -- this exercise has China in mind," he added.

India is nervous about the so-called "string of pearls", the concept of a network of ports around the Indian Ocean to which China's navy would have access, Yamamoto said.

"For India, this is a great threat," he said.

- Growing ties -

The manoeuvres also reflect growing ties between India and Japan, on both the military and economic fronts, with Japanese Prime Minister making an official visit to Delhi in January -- when the two nations agreed to "further strengthen" their defence cooperation and conduct regular naval exercises.

The July 25-30 exercises will include three Indian ships, a frigate, a destroyer and a supply ship, along with 700-800 personnel, Indian navy spokesman DK Sharma told AFP.

Sharma said the exercises would include anti-piracy, anti-terrorism, humanitarian assistance and helicopter drills.

"We just concluded... our naval drills with Russia, and since we have already travelled thousands of miles to that side, it's only natural that Japan will participate in the Malabar Exercise," he said.

The US Seventh Fleet, which covers the western Pacific and Indian Ocean, will take part in the war games while Japan is dispatching two escort ships, one US-2 search-and-rescue amphibious plane and one P3C patrol plane, said an MSDF spokesman.

He said several hundred Japanese personnel would take part.

"The purpose of Japan's participation is to improve the strategic capabilities of the MSDF and to strengthen the cooperation among the three militaries," he added.

China has lashed out at Abe after his cabinet formally endorsed a reinterpretation of Japan's pacifist constitution banning the use of armed force except in very narrowly-defined circumstances.

Beijing argued that it could open the door to remilitarisation of a country it considers insufficiently penitent for its actions in World War II.