China has demanded that Japan free 14 Chinese activists held after their protest landing on an island claimed by Tokyo.
Chinese Vice Foreign Minister Fu Ying "demanded that Japan ensure the safety of 14 Chinese nationals and immediately and unconditionally release them", the Chinese Foreign Ministry said on its website on Wednesday.
Japan, earlier on Wednesday, arrested the activists from the "Action Committee for Defending the Diaoyu Islands" group that sailed from Hong Kong, saying that they intented to plant a Chinese flag on an archipelago they know as Diaoyu, but which Japan calls Senkaku.
The boat made its landing, despite heightened security, including the firing of a water cannon at their boat, according to the protest group's leader.
The protest action coincides with the 67th anniversary of Japan's surrender at the end of World War II.
Prime Minister Yoshihiko Noda told reporters Japan would "deal with the incident strictly in line with the law".
"The Okinawa prefectural police arrested five men for violation of the immigration control law on Uotsurijima," a police spokesman told the AFP news agency, referring to one of the islands in the archipelago.
Seven people jumped into the water from their boat and were reported arrested several hours later by the Japanese Coast Guard spokesman.
"We have also arrested nine more people on suspicion of illegally entering our country.We have now taken a total of 14 people into custody and will carry out full investigation," the spokesman said.
All those arrested were being sent to the Okinawa main island for investigation, reports said.
Hong Kong leader Leung Chun-ying said he will "closely" monitor the incident and that the city's immigration officials will be in Japan to provide assistance to the activists.
"Japan must ensure the personal safety of the activists, especially the Hong Kong residents," he told reporters.
"Our stance on the territorial dispute is clear: the Diaoyu islands belong to China all this while," he added.
Japan's foreign ministry said it had summoned the Chinese ambassador to Tokyo to register its displeasure at the landing.
Beijing countered by saying it would lodge a complaint over the arrests.
The activists, who belong to the Action Committee for Defending the Diaoyu Islands, had said the move was aimed at countering a plan by a group of Japanese lawmakers to visit the disputed islands this weekend.
"We're very happy, we have tried many times and we declare this trip a big success," Action Committee for Defending the Diaoyu Islands spokesman Chan Yu-lam told reporters in Hong Kong.
"They [the Japanese] are like thieves, they take away the Diaoyu islands from us and they tried to stop us. They're like a thief shouting 'stop thief'," he said, using a Chinese proverb.
Tokyo is embroiled in an increasingly bitter spat with South Korea over another archipelago.
Pro-China groups have made repeated attempts to reach the islands, but apart from one successful foray in 1996 and one in 2004, they have been blocked by Japanese patrol vessels.
Also on Wednesday, two Japanese cabinet members visited the Yasukuni shrine to mark the anniversary of the country's World War II surrender, ignoring calls to avoid the shrine.