Rescuers wait outside the Songzao Coal Mine near Chongqing, in southwest China on September 27, 2020.
CNN  — 

At least 16 workers in southwest China were killed after they became trapped underground in a coal mine and exposed to unsafe levels of carbon monoxide, Chinese state media reported.

There were 17 people inside the Songzao coal mine in the Chinese city of Chongqing at the time of the incident, according to the state-run CGTN broadcaster. Only one person was pulled out alive by rescuers and they are in critical condition in hospital, CGTN reported.

The accident happened just after midday local time on Sunday, when a conveyer belt in the mine caught fire, producing excessive levels of carbon monoxide and trapping the miners.

State news agency Xinhua reported that carbon monoxide levels inside the coal mine had exceeded safe limits.

China’s Ministry of Emergency Management said in a statement that they are working to identify the cause of the accident and implement safety measures.

Ambulances wait outside the Songzao Coal Mine after workers became trapped.

A team led by the deputy director of the National Coal Safety Supervision Bureau was sent to guide the rescue and recovery effort at the mine, the ministry said.

The facility is owned by state energy firm Chongqing Energy. Managers at the Songzao coal mine had previously been fined and issued with warnings over safety violations at the site.

In late 2019, the Chongqing Coal Mine Safety Supervision Bureau issued “administrative penalties” and fines ranging from $700 to $4,200 to seven people for using improper mine blasting methods, according to a statement released by the bureau.

Mining accidents are not unusual in China. In 2017 there were 219 coal mining accidents in total, according to official statistics, killing 375 people. In 2018, the death toll from coal mine accidents stood at 333.

CNN’s Beijing bureau contributed to reporting