Four Chinese ships entered waters around islands at the centre of a bitter dispute with Japan on Saturday with no sign of a compromise seen between Asia's two largest powers.

The four Chinese coastguard vessels sailed into the 12-nautical-mile territorial waters around the Tokyo-controlled Senkaku islands -- which Beijing calls the Diaoyus -- Saturday morning, the Japanese coastguard said.

They had all left the waters more than four hours later and were in contiguous waters just outside of the 12-nautical-mile band Saturday afternoon, the Japanese guards said.

The moves came after the first anniversary Wednesday of Tokyo's nationalisation of part of the chain. On the eve of the anniversary, a flotilla of eight Chinese ships entered the territorial band of waters.

Often-testy ties have soured dramatically over the last 12 months, with frequent confrontations between official ships from both sides.

Japanese Prime Minister Shinzo Abe on Thursday vowed to beef up his country's defence capability amid the row with China.

Japan annexed what it says were the unclaimed islands in 1895. It says China's assertion of ownership only came after the discovery of resources in the seabed at the close of the 1960s.

Beijing maintains that the islands have been its territory for hundreds of years and were illegally snatched by Tokyo at the start of an acquisitive romp across Asia that culminated in World War II.