The Foreign Ministry said on Friday that the landing of two Japanese citizens on the Diaoyu Islands has seriously violated China's territorial sovereignty.
A Japanese coast guard official said on Friday that two Japanese nationals landed on the islands on Thursday, despite warnings from the coast guard to stay away.
"Despite our warnings, they dived into the sea from a fishing boat and reached the islands," the official said, adding that the two stayed for 90 minutes before leaving.
Media reports said the two Japanese right-wing activists went ashore on Beixiaodao, an islet of the Diaoyu Islands.
One of the two people who landed on the islands was Hitoshi Nakama, a local politician from Ishigaki, Okinawa. He also landed on the islands in January.
The case is under investigation by both the coast guard and police, the official said.
"The illegal acts of the Japanese right-wingers have seriously violated China's territorial sovereignty. China has lodged a solemn representation and protest to the Japanese side," Foreign Ministry spokesman Liu Weimin said at the ministry's regular news conference.
"The Diaoyu Islands and its affiliated islands have been Chinese territory since ancient times and China has indisputable sovereignty over the islands," Liu said.
The incident came one day after Taiwan vessels tangled with Japanese patrol ships in waters close to the islands and left a Chinese national flag on waters 10 meters from the shore.
"The Japanese move should be seen as a reaction to the visit of Taiwan vessels to the Diaoyu Islands," said Zhou Yongsheng, a professor of Japanese studies at China Foreign Affairs University in Beijing.
Ties between Beijing and Tokyo were tested in the autumn of 2010 when a Chinese trawler collided with patrol boats from the Japanese coast guard in waters near the islands. China later froze bilateral high-level exchanges, including some military ones.
