Rescuers are seen at the accident site after a coal and gas outburst happened at Zimujia coal mine in Panzhou City, southwest China's Guizhou Province, Aug. 7, 2018. Four people were killed and nine others remained missing after the accident occurred Monday evening. (Xinhua/Ou Dongqu)

Four people were killed and nine others remain missing in a coal mine accident in southwest China's Guizhou Province, local authorities said Tuesday.

The coal and gas explosion occurred around 9:10 p.m. Monday in Zimujia coal mine in Panzhou City.

The emergency rescue headquarters said the gas density in the mine had been lowered to less than 1 percent from the peak of nearly 40 percent. More than 60 rescuers are searching for the missing underground.

The mine belongs to Zhongrong International Trust Co. Ltd., with a designed production capacity of 300,000 tonnes a year. Its safety license expires in September 2019.

A citywide safety check has been launched in all coal mines.