TOKYO -- Tokyo city officials intending to buy tiny islands at the centre of a longtime territorial dispute with China left by boat on Saturday to survey the area ahead of the purchase they hope will bolster Japan's claim.

The five uninhabited islands in the East China Sea that are controlled by Japan but also claimed by China and Taiwan have become a major symbol of patriotic pride for some people in China and Japan. They are near key sea lanes and are surrounded by rich fishing grounds and untapped natural resources.

Tokyo Gov. Shintaro Ishihara has raised 1.45 billion yen ($19 million) in private donations over the last several months to buy the islands, known as Senkaku in Japan and Diaoyu in China, from individual Japanese owners.

Ishihara, a popular nationalist, told reporters Friday he had spoken with Prime Minister Yoshihiko Noda and offered to turn over ownership of the islands to the central government for free.

Supporters think having the government own the islands will strengthen Japan's control over them and send a tougher message to China. Noda said he would consider the offer but did not have an immediate reply, Ishihara said.

The city government says the purpose of the trip by a team of 25 experts and officials is to survey the area to assess its real estate value in preparation for the purchase. The central government did not grant permission to land on the islands, possibly to avoid a flare-up of tensions with China.

The boat left southwestern Japan late Saturday and is to circle the islands for about 10 hours on Sunday to study the area, examine animal and plant life, and measure the depth of coastal waters, according to the city government.

Ishihara wants to eventually build a lighthouse, a dock and a weather observatory on the islands. He has expressed interest in personally going to the islands, possibly next month, but is not part of this voyage.

Last month, Japan detained and later released 14 Hong Kong activists who landed on the islands. Japanese activists have made similar trips. One such group, including several lawmakers, landed a few days after the Chinese were detained.

Hundreds of Chinese have staged anti-Japanese demonstrations in several Chinese cities over the islands. Anti-Japanese sentiments run deep in China because of bitter memories of atrocities committed by Japanese soldiers during World War II.

This past week, a car carrying the Japanese ambassador to China was attacked by a man who ripped the Japanese flag off. No one was injured.