Japanese police on Wednesday arrested five men, a spokesman said, after pro-China activists landed on a disputed island in the East China Sea.

"The Okinawa prefectural police arrested five men for violation of the immigration control law on Uotsurijima island," he told AFP, referring to one of a chain of islands known as Diaoyu in China and Senkaku in Japan.

The arrest came shortly after seven pro-China activists jumped into the water from their boat and reached the rocky shore at about 5:30 pm (0830 GMT), local police and coastguard officials said.

Two of the activists then returned to their boat, they said.

A group of pro-China activists from Hong Kong and Macau set sail on a Chinese-flagged fishing boat from Hong Kong on Sunday, heading towards the disputed islands.

Japanese Prime Minister Yoshihiko Noda told reporters that he will "deal with the incident strictly in line with the law".

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.

The landing coincided with the 67th anniversary of Japan's surrender at the end of World War II. Tokyo is embroiled in an increasingly bitter spat with South Korea over another archipelago.

The activists made the landing despite the Japan Coast Guard's heightened security, which included firing water cannon at the activists' boat, said the protest group's leader.

Twelve Japanese ships had been following the fishing boat and a helicopter was hovering around, the leader said, but the coastguard declined to confirm the details for "operational reasons."

The pro-China group has made repeated attempts to reach the islands, but apart from one successful foray in 1996 they have been blocked by Japanese patrol vessels.

The uninhabited outcrops were the scene of a particularly nasty confrontation in late 2010 when Japan arrested a Chinese trawlerman who had rammed two of coastguard vessels.

Tensions spiked in April after controversial Tokyo Governor Shintaro Ishihara said his city intended to buy the islands from their private Japanese owner.