Authorities in northern China were investigating a coal mine operator with a focus on safety lapses, as rescuers searched for those missing in the country's deadliest coal mine explosion in recent years that killed at least 82 people.

An Associated Press reporter witnessed police and security guarding the entrance to the mining facility located in Qinyuan county in the city of Changzhi as emergency vehicles were onsite.

Hundreds of emergency responders and medical personnel were sent to help with rescue efforts, state media reported. Rescuers were taking turns to go down the mine shaft, according to the official Xinhua News Agency, facing hurdles including flooded tunnels.