China lodged a diplomatic protest with Tokyo on Tuesday after a visit by Japanese local officials to an island chain in the East China Sea claimed by both countries.

The protest over the uninhabited islands, known as Senkaku in Japan and Diaoyu in China, is part of a wider pattern of maritime territorial disputes between China and neighbours both citing historical and other claims over fishing areas and potential rich hydrocarbon deposits.

The Chinese government has already sent a stern message of protest to the Japanese side. I want to reiterate, the Diaoyu Islands and other related islands have been a part of China since ancient times, and China has indisputable sovereignty over them, foreign ministry spokesman Hong Lei said in a statement.(

Four people, including two local lawmakers representing Ishigaki city in Okinawa, landed on one of the disputed islands at around 0030 GMT on Tuesday, a Japanese Coast Guard official said.

Ishigaki city is, according to Japan, responsible for the administration of the islands.

The four walked around the coast for about two hours before leaving the island on a small rubber boat, the official said, adding that they may be subject to police questioning as Japan forbids anyone from landing on the islands.

The visit comes on the heels of Japanese Prime Minister Yoshihiko Noda's two-day trip to China in late December, where he and Chinese Premier Wen Jiabao agreed to set up a framework to discuss maritime issues.

Diplomatic ties between Beijing and Tokyo deteriorated sharply in late 2010 following Japan's arrest of a Chinese fishing boat captain near the disputed islands, though they have improved since then.

In 2008, Beijing and Tokyo agreed in principle to jointly develop gas fields near the islands, but progress has been slow and Japan has accused China of drilling for gas in violation of the deal.

(Reporting by Michael Martina and Yoko Kubota; Editing by Ed Lane)