A group of Japanese nationalists has made an unauthorized landing on a disputed island in the East China Sea, planting a Japanese flag and raising protests in several Chinese cities.

On Sunday, a group of 10 activists swam ashore and unfurled Japanese flags after a flotilla carrying about 150 people sailed to the island chain claimed by both Japan and China.

The landing came two days after Tokyo deported a group of Chinese that earlier travelled to one of the islands, planting a Chinese flag and singing China's national anthem.

Sunday's landing has fueled anti-Japan protests with thousands taking to the streets in several Chinese cities overturning Japanese cars and shouting slogans denouncing Japan's claims over the islands.

China has condemned Sunday's landing, describing it as an attempt to undermine the country's territorial sovereignty.

The group of uninhabited islands, known as Senkaku in Japanese and Diaoyu in Chinese, are a frequent flashpoint between Tokyo and Beijing. They are located in a gas-rich area and surrounded by rich fishing grounds.

The islands were administered by the United States from the end of World War Two until they were transferred back to Japan in 1972. They contain not only important natural resources, but are also a source of national pride in both Japan and China.