Tokyo city officials planning to buy tiny islands at the center of a longtime territorial dispute with China surveyed the area Sunday on a visit meant to send a message of ownership.

The boat, carrying 25 experts and officials as well as journalists from news organizations including The Associated Press, circled the five uninhabited islands in the East China Sea which are controlled by Japan but also claimed by China and Taiwan.

China responded quickly to the survey, saying any unilateral action by Japan on the islands is "illegal" and "invalid."

Tokyo city officials say the survey is crucial and includes measuring the water depth to build a dock at the islands, known as Senkaku in Japan and Diaoyu in China. Japan's central government did not grant permission to land on the islands.

Tokyo Gov. Shintaro Ishihara, a strong nationalist, has raised 1.45 billion yen ($19 million) in private donations over the last several months to buy the islands from the Japanese family that owns them. Supporters think having the government own the islands will strengthen Japan's control over them and send a tougher message to China.

"It is an undeniable fact that the islands are Japanese territory, so our task is to see how we can best maintain that," Yoshihiko Yamada, a special adviser to the city's team, said aboard the boat.

The team was scheduled to study the islands for about 10 hours Sunday before heading back to Okinawa in southwestern Japan.

The islands, a symbol of patriotic pride for some people in China and Japan, are near key sea lanes and are surrounded by rich fishing grounds and untapped natural resources.

China's Foreign Ministry said it had already 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.

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

Japan therefore has much to gain by avoiding tensions with China. But Ishihara remains extremely popular, having been re-elected as Tokyo governor three times following a stint in parliament.

Seiichiro Sakamaki, the leader of the Tokyo survey team, stressed that the city is going to buy the islands.

"The basic point is that those who are about to buy property need to look at it," he said.

Hundreds of Chinese have staged anti-Japan demonstrations in several cities over the island dispute. Anti-Japanese sentiment runs deep in China because of bitter memories of atrocities committed by Japanese soldiers during World War II.

This past week in Beijing, a man ripped the Japanese flag off a car carrying Japan's ambassador to China. Last month, Japan detained and later released 14 Hong Kong activists who landed on the islands. Japanese activists have made similar trips.


Associated Press writers Yuri Kageyama in Tokyo and Gillian Wong in Beijing contributed to this report.