China's largest offshore oil producer, China National Offshore Oil Corp., has reported that the Chunxiao gas field in the East China Sea near an area Japan claims is within its territorial waters, is now under full-scale production.

The announcement, published on the CNOOC's Web site, was attributed to Zhang Guobao, head of China's State Development and Reform Commission.

The Chunxiao field, called Shirakaba in Japan, is a few kilometers west of the Japan-designated median line, which Japan says should delimit the two countries' 200-nautical-mile exclusive economic zones.

Beijing does not recognize the line and claims its EEZ stretches to the edge of the continental shelf, near Okinawa, and encompasses Taiwan.

Japan is worried China may siphon off resources that may lie on its side of the line.

In January, CNOOC said it would be ready to start production in the Chunxiao field in the first half of 2006, but added at the time it would not unilaterally announce the start of production in light of the territorial dispute.