GUIYANG -- 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 pm 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.