There are about 60 such sites in China, Liu said.

The weapons are an enduring source of anger for Beijing, which says they have killed at least 2,000 Chinese since 1945.

Under a 1997 international convention, Tokyo is committed to disposing of its chemical weapons in China by 2007. But Liu said Beijing hopes to extend that by five years because the two governments have excavated weapons but haven't begun to destroy them.

"We're not satisfied with the speed of processing the abandoned chemical weapons by the Japanese side in China," Liu said.

Liu said Tokyo blamed the slowness of the process on lack of adequate numbers of chemical weapons experts and the complicated conditions in areas where they have been found.

"To some extent, the Chinese government understands the reasons they gave. But as the country that is suffering, we hope the Japanese government can speed up the process," he said.

The factory in Ning'an received poison-gas bombs in consignments of scrap metal sold by local people and buried them alongside other chemical weapons that were found on the grounds, according to Liu.

The bombs are to be moved to a newly built disposal facility in Harbaling, a city in neighboring Jilin province, where some 30,000 other chemical weapons already are stockpiled, Liu said.

In 2003, one person was killed and 43 others were injured when construction workers broke open a buried barrel of abandoned poison gas in Qiqihar, a city in northeast Heilongjiang province. It was the most serious incident in recent years.

Qiqihar was a major center for Japan's military operations.