A Hong Kong activist group set sail on Sunday for the Diaoyu Islands in the East China Sea, known as the Senkaku in Japan, in an attempt to join forces with counterparts from the mainland China and Taiwan to assert China's sovereignty over the islands. 

The official Global Times reported that the Action Committee for Defending the Diaoyu Islands set sail at noon from the Tsim Sha Tsui pier in Hong Kong with four crewmembers and 11 activists aboard, including one Macanese and one mainland Chinese.

Chan Miu-tak, chairman of the Action Committee for Defending the Diaoyu Islands, told Japan’s Kyodo News that their "protect Diaoyu" ship is expected to be joined at sea in Tuesday by two other vessels, one from Xiamen in southeastern China and the other from Taiwan, in a coordinated attempt to sail to the islands. August 15 is the memorial day of victory over Japan during World War II.

"Japanese lawmakers are planning to land on the islands on Aug. 19; we want to reach there before they do," Chan was quoted as saying. "[We will] place the [mainland] flag there to show our determination to safeguard China's sovereignty over the islands."

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

Despite its consistent assertions of sovereignty over the islets, the Chinese government has been reluctant to allow civilian protests to prevent direct conflict with Japan. Hong Kong has been doing the same.

The Hong Kong marine police has intercepted the ship and boarded it for inspection as the ship left the waters of Hong Kong, according to the Global Times. The activists locked up the command room and continued sailing, forcing the police to let them go, the report said.

The group said it has asked China escort the ship, noting that Taiwan sent coast guard vessels to escort and protect Taiwan activists when they sailed to the islands last month, Kyodo said.

"If Japan should strongly protest the South Korean president's visit (to the disputed islets), Beijing should also act strongly to protect Diaoyu islands," group member David Ko was qouted as saying by Kyodo.

Mainland activist Li Yiqiang said the Xiamen government had not yet responded to their application, the Global Times said.

Lv Yaodong, a researcher from the Institute of Japanese Studies at the Chinese Academy of Social Sciences, said 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, according to the Global Times.

The pro-China group has repeatedly tried to reach the islands. But apart from one successful foray in 1996, they have been blocked by Japanese patrol vessels, according to Hong Kong-based newspaper the Standard.

Both China and Japan claim sovereignty over the uninhabited islands, controlled by Japan in the East China Sea, which are located approximately200 nautical miles east of the Chinese mainland and 200 nautical miles southwest of the Japanese island of Okinawa.