Japan will deploy two more patrol ships to boost its defence of islands at the centre of a territorial row with China and has conducted its first drill simulating the recapture of an isle seized by enemy forces.

The vessels will be stationed at the regional coast guard headquarters which covers the Japanese-controlled Senkaku islands in the East China Sea, known as the Diaoyus in China, Japanese public broadcaster NHK said Monday.

The 335-tonne "Kurose" and the 3,100-tonne "Chikuzen", equipped with a helicopter, will be deployed in August and October respectively, NHK reported.

On Sunday, Japan's Ground Self-Defense Force carried out the nation's first military exercise designed to recapture "a remote island invaded by an enemy force," officials said.

Some 300 troops took part in the 40-minute drill with 20 warplanes and more than 30 military vehicles at the Narashino Garrison in Chiba, southeast of Tokyo.

Some 80 personnel from the SDF's First Airborne Brigade rappelled from helicopters with parachutes in front of some 11,000 spectators to demonstrate manoeuvres to counter an enemy invasion of a remote island.

"We will strengthen the deployment of the Self-Defense Force in response to the tougher security environment surrounding our country," Defense Minister Itsunori Onodera told the military.

Chinese government ships and planes have been seen off the disputed islands numerous times since Japan nationalised them in September, sometimes within the 12 nautical-mile territorial zone.

Tokyo's defence ministry has said that F-15s were sent airborne to head off Chinese state-owned -- but not military -- planes four times in December, including an occasion when Japanese airspace was breached.

They were also mobilised in January, it said.

Japan plans to spend an extra 180.5 billion yen ($2.0 billion) on missiles, fighter jets and helicopters, an official said last week, as it tries to strengthen defence capabilities with concerns growing over a rising China.

The announcement came after Prime Minister Shinzo Abe's ruling Liberal Democratic Party said Japan would increase military spending for the first time in 11 years in the next fiscal year starting April.