A ship belonging to a Hong Kong activist group set sail Sunday for the Diaoyu Islands in the East China Sea in an attempt to join forces with counterparts from the Chinese mainland and Taiwan to assert China's sovereignty over the islands.

The ship of the Action Committee for Defending the Diaoyu Islands set sail at noon from the Tsim Sha Tsui pier in Hong Kong with 15 people aboard, including four crewmembers and 11 activists, Yang Kuang, a long-time activist and captain of the ship, told the Global Times.

Among the 11 activists, one came from Macao, one from the mainland, and the rest from Hong Kong.

According to an announcement posted on the activists' website, the ship sailed off the waters of Hong Kong at 8:30 pm after spending hours at the Sai Kung pier for maintenance.

According to the activists, the Hong Kong marine police intercepted the ship and boarded it for inspection while the ship was on its way to leaving the waters of Hong Kong. The activists locked up the command room and continued sailing, forcing the police to let them go.

The activists expect to meet the vessels of their Taiwanese counterparts in the Taiwan Straits in two days, and then from there head to the Diaoyu Islands together.

"We plan to reach the islands on August 15, the memorial day of victory over Japan during World War II," said Yang.

Li Yiqiang, a mainland activist, told the Global Times Sunday that vessels from the mainland will set off from Fujian Province if the government approves their action. Li refused to reveal more details as the government had not yet responded to their application.

Chan Miu-tak, chairman of the Hong Kong activist group, told the Global Times that this voyage was a response to some 50 Japanese lawmakers' plan to set foot on the Diaoyu Islands on August 19.

The Japanese lawmakers are planning to hold a vigil for the victims of a refugee shipwreck during World War II on the islands, reported the Ta Kung Pao paper.

According to Japanese media, the Japanese Coast Guard has heightened alert and reinforced patrols in waters near the Diaoyu Islands, in the wake of the Chinese activists' trip.

Lü Yaodong, a researcher from the Institute of Japanese Studies at the Chinese Academy of Social Sciences, told the Global Times that the Japanese government must understand that their recent actions surrounding the islands have triggered widespread discontent among the Chinese population, and Japan's claim over the islands could threaten peace in East Asia.