Chinese media are reporting that 33 coal miners trapped underground after a gas explosion have been found dead. Rescuers in the southwest Congqing region of China had worked since Monday to reach the miners, just two of whom escaped alive. By Wednesday morning, rescuers had reached the site of the underground explosion and pulled all the bodies to the surface. It’s still unclear what caused the blast, but typically they’re started when an electrical spark ignites built up gas leaking from the ground and into the mine shaft. The mines are supposed to be ventilated to prevent these explosions, but these accidents have become fairly common in Chinese mines. China is the world’s largest producer and consumer of coal. Poor oversight and regulation has also made it one of the world’s deadliest places to be a miner. As part of its plan to reform the industry, China’s State Administration of Work Safety said earlier this year it would close more than 1,000 outdated mines. In this latest incident, safety officials said they’d conduct an investigation into the explosion and punish those found culpable.