Coastguard vessels from Taiwan and Japan "bumped into" each other in waters near a disputed island chain Wednesday, as the Taiwanese vessel was escorting activists to the area, Japan's coastguard said.

The Taiwanese vessel was part of a small flotilla that had been accompanying a fishing boat carrying at least nine activists to waters near islands known as Diaoyu in Chinese and Senkaku in Japanese.

One of the four Taiwanese patrol ships carried a Japanese-language banner reading: "This is territory of the Republic of China," a Japanese coastguard official said.

The five Taiwanese vessels entered waters Japan claims as its territory shortly after 7 am (2200 GMT) and left the area by noon Wednesday, the official said.

"The boat, moving in the same direction as one of the Japanese patrol ships, bumped into it and scratched the paint," the official said. "There were no injuries in the incident."

Taiwanese activists entered waters near the disputed islands in 2008, also escorted by two of Taipei's coastguard ships, he said.

The disputed islands are also claimed by China, and are occasionally the focus of tensions between Tokyo and Beijing.

A particularly nasty confrontation in late 2010 saw Japan arrest a Chinese trawlerman who had rammed two of its patrol vessels.

A weeks-long stand-off only ended when Japan released the captain, in a move widely seen as a diplomatic black eye for Tokyo.

Tokyo's controversial nationalist governor launched a fund earlier this year to raise cash for the metropolis to buy the islands from their private Japanese owner, charging the government was not doing enough to protect territory.