TOKYO - JAPAN protested on Monday after two Chinese marine survey ships entered what it considers its waters, with Tokyo's top government spokesman describing the incident as 'extremely regrettable'.

'Such activities by Chinese ships are extremely regrettable. We are demanding the Chinese government order their immediate withdrawal,' Chief Cabinet Secretary Takeo Kawamura told reporters.

Meanwhile, Japan's coast guard urged Chinese survey ships to leave waters near disputed islands in the East China Sea, and the government lodged a protest with Beijing, officials said.

The two maritime survey ships entered waters surrounding the Japan-held islands, known as the Senkaku in Japan and the Diaoyu in China, earlier in the day, the coast guard said.

'Despite repeated warnings issued by radio from our patrol boat, the Chinese ships are still within our waters,? said coast guard official Kazuya Ono.

Beijing responded to Japan's protest by saying it was checking facts, a Japanese Foreign Ministry official said on condition of anonymity, citing protocol.

The islands are held by Japan but claimed by China and Taiwan, and the territorial dispute is one of many that have strained ties between Tokyo and Beijing.

It was unclear what the Chinese ships were doing in the waters, which Japan watches closely for intrusions by outside ships.

In June, a Taiwanese fishing boat sank near the islands after a collision with a Japanese coast guard ship. Taiwan accused the Japanese of ramming the boat; Japan contended the Taiwanese captain was responsible for the collision.

Japanese authorities recently agreed to give the sunken ship?s owner 10 million New Taiwan dollars (S$535,000) in compensation.

Japan annexed the island chain in 1895, saying no nation exercised a formal claim over them. The islands, lying roughly midway between Okinawa and Taiwan, were administered by the United States after World War II until they were returned to Tokyo in 1972.

China says the islands have been part of its territory since ancient times. -- AFP, AP