"They have no special symptoms, they are in stable condition and under observation," an official surnamed Song at the Number 1 Hospital of the Qiqihar Medical University in Heilongjiang province told AFP.

According to Xinhua news agency, the workers dug up a canister at a construction site in the city's Fulaerji district on Monday afternoon.

Strong odors coming from it led local military experts and police to believe it was mustard gas left by Japan's retreating army during World War II, and they sealed the site.

In August 2003, a similar incident in the same city killed one, hospitalized 43 others and ignited a diplomatic row between China and Japan.

Japan eventually paid some 2.8 million dollars in compensation for the incident.

Tokyo estimates that 700,000 chemical bombs and grenades were abandoned in China by its retreating armies, although Chinese experts put the figure at up to two million -- the world's largest stockpile of abandoned chemical weapons.

Tuesday's report comes after a high court in Tokyo overturned a lower court ruling that had awarded some 1.45 million dollars in compensation to Chinese that were forced into labor by Japanese companies during World War II.

WAR.WIRE