China has full sovereign and jurisdiction rights over the Chunxiao oil and gas field and Beijing's activities there are entirely reasonable and legitimate, Foreign Ministry spokeswoman Jiang Yu said on Friday.

Earlier, Japanese media reported that China had transported equipment into the Chunxiao field in the East China Sea and said it was probably about to carry out maintenance work there.

Jiang neither confirmed nor denied the reports but said China has every right to be active in the Chunxiao field.

Jiang added that China had "sent marine surveillance ships to strengthen law enforcement in Chinese related waters to protect maritime rights and interests".

"China's related departments have also sent fishery administration ships to China's territorial waters to provide protection to fishermen," Jiang said.

She made the comments when asked to confirm whether China's marine surveillance ships had demanded that Japan stop marine surveying activities in related waters and whether China's fishery administration ships had enhanced law enforcement activities in the areas.

A Chinese fishing boat was in collision with two Japan Coast Guard patrol ships in waters off the Diaoyu Islands in the East China Sea on Sept 7.

The seizure of the Chinese trawler and its crew by the Japan Coast Guard developed into a diplomatic crisis between China and Japan.

China has repeatedly lodged protests with Japan about the incident.

Fourteen Chinese fishermen and the trawler subsequently returned home on Monday, but the captain was still being held by Japan.

The Chinese government declared it was postponing negotiations with Japan aimed at signing a treaty over joint gas field exploitation in the East China Sea.

The two governments had planned to hold a second round of negotiations on the issue in mid-September in Beijing after the first round of talks had been held in Tokyo in late July.

Beijing and Tokyo had reached a broad agreement in June 2008 to resolve disputes in the East China Sea by jointly exploring the fields.

The two sides reached a basic understanding on the joint development.

However, due to differences over the proportion of investment and the distribution of interest, there has been no further development since 2008.