Fishermen in April will begin catching tuna near Okinotorishima, 1,730 kilometers southeast of Japan's capital, Tokyo metropolitan government official Kiyoshi Nakamura said. The capital claims the territory falls under its jurisdiction.

``Of course, the territorial issue is important, but once we start the project we will explore a new, rich fishing ground,'' Nakamura said.

The tiny territory is made up of two outcroppings that Japan has fortified with concrete against the encroaching waves. The area is considered rich in undersea natural resources, but fishing has hardly been conducted in the area.

Japan says the outcroppings are proper islands and argues that they extend the country's exclusive economic zone.

But China says they are only rocks, and therefore cannot be used by Tokyo to extend the zone. An economic zone extends 200 nautical miles, or 370 kilometers, from the shore of a country's territory.

Word of the expeditions comes less than a week since Japan took over a lighthouse built by a right-wing political group on a separate island that is also claimed by the mainland and Taiwan.

The government said the move on the islands, called Senkakus by Japanese and Diaoyus by the Chinese, was not politically motivated, but Beijing called the Japanese actions ``illegal and invalid.''

The tussle over Okinotorishima flared late last year when a Chinese research ship twice came within 200 nautical miles of the territory, triggering a diplomatic protest by Japan. China said the ship was conducting scientific exploration on the ``high seas.''

The issue has riled nationalist sentiment in Japan. Outspoken Tokyo governor Shintaro Ishihara has urged Japan to step up territorial claims over the island and nearby waters.

Japanese public broadcaster NHK reported that Japan is considering beefing up marine and meteorological research on Okinotorishima and possibly posting full-time staff there to boost its claim for island status.

Prime Minister Junichiro Koizumi's government has also earmarked about 23 billion yen (HK$1.7 billion) to explore natural gas fields in the disputed area, where China has also been surveying.

The United Nations Convention on the Law of the Sea, which both countries have signed, allows coastal countries an economic zone extending 200 nautical miles from their shores.

But Beijing and Tokyo have not agreed where their sea border lies.

The UN says it will decide on global offshore territorial claims by May 2009.

Relations between Japan and China have been especially rocky in recent years. In addition to territorial disputes, the two countries are sparring over interpretations of World War II history. ASSOCIATED PRESS