The plan calls for the dispatch of 55,000 troops as well as warplanes, destroyers and submarines from Japan's main islands in the event of an attack on Okinawa and other remote islands, Kyodo news agency reported.

The national defense agency compiled the plan covering the islands lying in a 1,000-kilometer (625-mile) zone between the southern tip of Japan's Kyushu Island and Taiwan, Kyodo said, citing unspecified official documents.

In November Japan made public its new defense guidelines which explicitly point to China as a potential threat for the first time along with North Korea.

A Defense Agency official said that Japan's defense forces "do not have troops stationed on most of the southern remote islands and they are a vacuum in terms of security," according to Kyodo.

"China has been expanding its scope of activities as seen in the case of an invasion of Japanese territorial waters (by a Chinese nuclear submarine) last November. We need to monitor its moves," the official was quoted as saying.

Under the new plan, naval patrol planes and the airborne warning and control system of the air defense force will collect information on the remote islands, the report said.

Of the 55,000 troops, 9,000 will be assigned to directly recapture invaded islands with the rest providing support for them, the report added.

Japan has been increasingly alarmed by the expanding military capabilities of its communist neighbours China and North Korea.

The guidelines said: "China, which has a great impact on security in this region, is pushing ahead with enhancing its nuclear and missile capabilities in modernizing its navy and air force while expanding marine activities."

Meanwhile, Japan has been pushing for a missile defense shield with the United States after North Korea lobbed a suspected ballistic missile over its territory and into the Pacific in 1998.

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