TOKYO - Tokyo city officials planning to buy tiny islands at the centre of a longtime territorial dispute with China surveyed the area and took water samples, in a showcase meant to send a message of ownership.

Tokyo governor Shintaro Ishihara dispatched the 25-member team, who yesterday arrived at the island chain, known in China as Diaoyu and in Japan as Senkaku.

Mr Ishihara, known for his outspoken views, wants to buy them from their private owners to highlight Japan's claim and build a small harbour for fishing vessels.

The team remained on their boats to survey the shoreline and waters around the rocky uninhabited isles, Japanese TV showed.

The national government rejected their request to land on the islands.

"Seeing it with your own eyes is different from seeing them on a map," Mr Seiichiro Sakamaki, the Tokyo official leading the team, told Japanese television networks as he stood aboard a survey ship near the islands.

"The scale and size are very clear to see. The governor has asked what could be done to build a small harbour. We want to check the islands with that in mind," he said.

Mr Ishihara, a vocal critic of China, has previously said he hopes to visit the islands himself in October when he sends another survey mission.

Chinese state media said the surveyors were acting "illegally", describing yesterday's mission as the "latest provocative move that infringes on Chinese territory".

China's foreign ministry said it had made "solemn representations" to Japan about the visit.

"The Chinese side reiterates that any unilateral action by the Japanese side on the Diaoyu islands is illegal, invalid, and will not change the reality that the Diaoyu islands and its affiliated islands belong to Chinese territory," it said in a statement.

Testy Japan-China ties turned for the worse last month after activists, mostly from Hong Kong, landed on one of the islands, which are controlled by Japan. They were arrested by the Japanese authorities and deported.

Japanese nationalists raised their country's flag on the island days later, prompting protests in cities across China.

Despite the squabbling over the islands, economic ties between China and Japan are growing. Major Japanese manufacturers, such as Nissan Motor and Sony, are eager to get a slice of the Chinese market, while ailing companies like Sharp, which makes flat panels for TV sets, are wooing Chinese investment.

AGENCE FRANCE-PRESSE, ASSOCIATED PRESS