About 18 coal miners have been killed by excessive levels of carbon monoxide in southwest China, according to state TV.
Only one out of 24 workers have been found alive following the disaster on Friday in the Diaoshidong mine in Chongqing municipality, officials says.
A rescue operation is underway in search of five other workers, with police officers and firefighters on the scene.
Broadcaster CCTV said the lethal gas leak occurred while workers were deconstructing underground equipment, and that an investigation has been launched into the cause of the accident.
The facility, established in 1975, has an annual production capacity of around 120,000 tonnes of coal. In March 2013, hydrogen sulfide poisoning left three dead and another two injured in the mine.
The official Xinhua news agency said that the incident at Diaoshidong is the region’s second such accident in just over two months.
In September 2020, 16 workers were killed when a conveyor belt caught fire at another mine in the municipality, producing similarly toxic levels of carbon monoxide.
In December 2019, an explosion at a coal mine in Guizhou province, also in southwest China, left 14 people dead.
China’s coal mining industry used to be the world’s deadliest, suffering more than 5,000 fatalities a year.
Safety has improved dramatically after authorities started efforts to overhaul the industry around 15 years ago.