China's protest came during a meeting between Vice Foreign Minister Wang Yi and Japanese Ambassador Koreshige Anami, state television said.

"The chemical weapons discarded by Japan in Qiqihar has posed a serious threat to the local people," Wang was quoted as telling the Japanese ambassador.

Thirty-five people were affected and two were in a critical condition at a hospital in Qiqihar, Heilongjiang province after they came in contact with five barrels of toxic mustard gas at a construction site in the city last week.

Last Friday, China lodged a formal protest with Japan over injuries to the workers who discovered on August 4 the drums of mustard gas allegedly buried by retreating Japanese armies nearly 60 years ago.

Japan dispatched four officials to the city on Sunday to investigate and vowed to appropriately handle the aftermath.

Japan's brutal occupation of Chinese territory before and during World War II remains a source of tension between the countries with more than 700,000 chemical weapons estimated by Japan to have been abandoned by their retreating armies in the months around their surrender.

Chinese experts say that as many as two million such weapons are still buried, giving China the world's largest stockpile of leftover chemical weapons.

WAR.WIRE