Chinese Foreign Ministry spokesman Liu Jianchao said Thursday that any unilateral action taken by Japan on the Diaoyu Islands are "unlawful and invalid."

China "firmly opposes" such moves, which seriously infringes China's territorial sovereignty, Liu told a regular press conference.

It is reported that some Japanese members of the Ishigaki assembly in Okinawa Prefecture proposed to enact an ordinance on so-called "Senkaku Day". Senkaku is the name used by Japan on the Diaoyu Islands.

China expressed severe concern over the act and has stated China's solemn stance to the Japanese side through diplomatic channel, he said.

Liu reiterated that the Diaoyu and surrounding islands have been a part of the Chinese territory since ancient time. "China holds indisputable historical and lawful evidence" on the issue, he said.