China has retracted a statement that it has begun production at an oil and gas field in the East China Sea in an area disputed with Japan, Japanese officials said Monday.

China National Offshore Oil Corp (CNOOC) said on its website last week that the first stage of gas production had begun at the Chunxiao field.

But Japanese officials said the statement had been removed from the website after Japanese media began reporting about it at the weekend.

"We have tried to verify the information and learned that there is no truth in it," Vice Japanese Foreign Minister Shotaro Yachi told a news conference.

Deputy Chief Cabinet Secretary Masahiro Futahashi said the Chinese side had told Japan there was no change at the field.

CNOOC, China's biggest offshore oil producer, had said Zhang Guobao, vice chairman of China's National Development and Reform Commission, had inspected the field last month and urged CNOOC to make good use of the resources.

"The first phase of Chunxiao oil and gas field has already entered the production stage," Zhang was quoted by the website as saying.

Chief Cabinet Secretary Shinzo Abe, the top Japanese government spokesman, said earlier Monday that Tokyo had asked Beijing last Friday to check the information.

"At the same time, we requested anew that China halt the exploration project and provide Japan with information," Abe said, adding that it was confirmed on Monday that the statement on the webside had been deleted.

Japan and China have long disputed their sea border and Beijing has always insisted its exploration in the East China Sea is within its territorial waters.

But Japan says the gas field lies too close to its Exclusive Economic Zone — a delineation not recognized by China — and fears China might siphon off resources from an area Japan claims as its territory.

A 1999 Japanese survey estimated there were 200 billion cubic meters (seven trillion cubic feet) of gas reserves in the area.

Tensions escalated last year after Japan said it had spotted flames indicating China had started production near the area where Japan claims development rights. China began test-drilling in 2003.

The two countries failed to find common ground during many rounds of talks, with China saying "great differences still remained" after the last round in July.

The energy reserves are among a number of disputes that have badly damaged relations. They are also divided by the legacy of Japan's wartime militarism in the region.