A group of Hong Kong activists set sail Sunday for a cluster of Japanese-controlled isles in the East China Sea to assert China's sovereignty over them.

"Japan out of the Diaoyu islands! Down with Japanese militarism!" the activists chanted as dozens of mainland tourists and local residents looked on at Tsim Sha Tsui pier before the protest vessel Bao Diao II set sail.

Chan Miu-tak, chairman of an activist group called Action Committee for Defending the Diaoyu Islands, said the "protect Diaoyu" boat will be joined at sea on Tuesday by two other vessels, one from Xiamen in southern China and another from Taiwan, in a coordinated attempt to sail to the islands, known as the Senkaku in Japan, Diaoyu in China, and Tiaoyutai in Taiwan.