The Chinese government is demanding that Japan shoulder responsibility after a number of people in northeastern China were sickened by poison gas left by Japanese troops during the Second World War.
Reports of a mass poisoning emerged last week after workers in the northeastern city of Qiqihar found and accidentally punctured canisters of poison gas.
Chinese official media say at least 34 people had to be hospitalized after complaining of headaches, burning eyes, and other symptoms.
Japan has acknowledged that its troops had abandoned the canisters at the end of World War II, nearly six decades ago. The Japanese Foreign Ministry issued a statement calling the accident "extremely regrettable."
Japanese officials say Japan will commit to clean up any chemical weapons its troops left behind. Officials say they will cooperate closely with Chinese authorities.
China's Foreign Ministry this week summoned the Japanese ambassador, who expressed regret over the poison gas leak. Chinese officials say China had taken note of Japan's willingness to take responsibility for the incident.
A high ranking Foreign Ministry official has called on Japan to speed up efforts to clean up chemical weapons throughout the parts of China it occupied during the war.
China and Japan maintain cordial relations. But there remains much resentment among Chinese over the atrocities committed by Japanese troops during their occupation of much of China.
Incidents such as the discovery of leftover poison gas often reignite anger because Japan has never formally apologized for its past aggression against China.