China has protested after a Japanese coastguard ship fired a water cannon at two boats carrying Chinese activists near the disputed Senkaku islands.
About 20 Chinese activists are on board two fishing boats
China's state-run Xinhua news agency said the Japanese boat's action injured at least one of the 20 people on board.
A Coast Guard spokesman said it acted after asking the boats to leave Japanese territorial waters.
The islands are administered by Japan but claimed by China, which calls them the Diaoyu Islands.
The incident sparked a small protest outside the Japanese embassy in Beijing and a complaint from the Chinese government.
Xinhua quoted an organiser of the trip saying that the boats had been targeted on Thursday night under cover of darkness.
"Under attack by high-pressure water cannons, the glass of the control cabin of a boat burst into pieces, leaving the face and hand of one boatman injured by broken pieces of glass," Li Nan, was quoted as saying.
A Japanese coastguard spokesman said that he was not aware of any injuries and that only one water cannon was fired, after a rock was thrown from one of the protest ships.
The Chinese reports said 10 Japanese ships and a plane had been in the area at the time.
China and Taiwan both laid claim to the Senkaku Islands in the 1970s after oil deposits were found nearby.
They were declared Japanese territory in 1895 and fall under the jurisdiction of Japan's southern Okinawa prefecture.
In recent years a number of expeditions to the islands have been launched by activists claiming them as Chinese territory.
The two ships on the latest protest set off from China's southern coastal city of Xiamen on Tuesday night flying banners which said: "Chinese territory, Japanese get out".