Japan is putting missiles on islands marking the gateway to the Pacific, officials said Thursday, as part of a huge military drill that has unsettled Beijing.

The exercise, aimed at bolstering Japan's defence of remote islands, has already seen a launching system and a loader for Type-88 surface-to-ship missiles installed on Miyako island, complete with two missiles.

Four more missiles were due to arrive on the main island of Okinawa later Thursday. It was not clear how long they would remain in place.

"This is the first time" that missile systems have been taken to Miyako, said a spokesman for the Joint Staff of the Self Defence Forces, adding that the missiles could not be fired in their present state.

"The drill is designed for the defence of islands," he said.

While the Japanese military makes no secret of the fact these missiles are not operable, observers say their deployment serves to remind anyone watching of Japan's capabilities.

The Self Defense Forces began their 18 days of war games on November 1, with 34,000 military personnel, six vessels and 360 aircraft.

The exercise comes amid growing nervousness in Japan and other parts of Asia over China's surging military might, which has seen it expand its naval reach into the Pacific Ocean as it squabbles with Tokyo over the ownership of islands in the East China Sea.

Beijing also has separate disputes with numerous countries over competing claims in the South China Sea. It claims most of the sea as its territory.

Chinese naval assets stationed in the north of the country are somewhat hemmed in by the chain of Japanese islands that separate the East China Sea and the Pacific.

The strait between Miyako and the main island of Okinawa offers one of the few direct access points to the ocean.

The Japanese drill would bring the roughly 300-kilometre (190-mile) stretch between the main Okinawa island and Miyako under the missiles' presumed range, Japanese media reported.

Tokyo has said the drill is not aimed at any specific nation, but Japanese leaders have openly expressed disquiet as China escalates its territorial claims.

The Self Defence Forces are also preparing to form a special amphibious unit, much like the US Marine Corps, whose remit would be to defend small islands and recapture them in case of enemy attacks.

Beijing has routinely sent government vessels to disputed islands in the East China Sea, staging dangerous face-offs between the two nations' coastguards.

In the latest incident, four Chinese coastguard vessels on Thursday entered territorial waters off one of the Tokyo-controlled Senkaku islands -- which Beijing calls the Diaoyus. They remained for around 90 minutes, Japan's coastguard said.

Relations between Asia's two largest economies have frayed badly over the last year, with the islands the ostensible focus of a dispute that is fanned by nationalism on both sides.

For China, the row is also fuelled by unresolved historical grievances, while Tokyo is on edge over what it sees as a sometimes hostile neighbour whose military is expanding at a real lick.

The ongoing Japanese drill has irritated Beijing, where local media said there was no doubt it was aimed at China.

The Global Times newspaper, which is close to the ruling Communist Party, reported on its front page Thursday that Japan's decision to bring the missiles to Miyako was "an unprecedented move that experts say is targeted at blocking the Chinese navy".

"The missile deployment is mainly set against China and it can pose real threats to the Chinese navy," Li Jie, an expert on China's navy, told the paper.

Beijing's military, through state media, has accused Tokyo of interfering in Chinese live-fire drills in the Pacific last month, an allegation that Japan denied.