Six people are dead and 47 missing after a slope collapsed at an open-pit coal mine in North China's Inner Mongolia autonomous region, the rescue operation headquarters said on Thursday.

Police have detained those in charge of the mine and an investigation has been launched to determine the reason for the accident at the mine in Alshaa League, which happened around 1 pm on Wednesday. The results of the investigation will be released in due course, said officials from the headquarters.

Detailed information has been obtained about the missing workers, and the rescue headquarters has arranged for their relatives to be contacted.

As of 10:30 pm on Thursday, rescue workers had found 12 people. Six of them were injured and sent to the hospital. The injured are all in stable condition.

Due to a lack of medical facilities near the site, the Qingtongxia People's Hospital in the Ningxia Hui autonomous region, about 60 kilometers from the mine, has been designated to treat the injured.

According to the rescue headquarters, experts from the national emergency medical rescue team and the hospital have formed a medical team to treat the injured. A blood bank has been established to ensure enough supplies for treatment.

Ma Jianping, one of the injured, recounted what happened when the slope collapsed. "We had just gone to work at that time and noticed that some rocks were falling from the slope, and then the situation got worse," he told China Central Television. "We were organized to evacuate (the site), but it was too late and the slope collapsed."

According to the rescue headquarters, 19 rescue teams, 919 rescue workers and more than 200 sets of equipment are being used in the operation to find the miners. A restricted zone has been set up around the accident area and equipment put in place to monitor any slope collapses.

The coal mine, which is run by Xinjing Coal Industry Co, used to be an underground mine. It was converted into an open-pit mine in 2012 and production resumed in April 2021 after being suspended for three years, the rescue headquarters said.

Over the years, the mining operations formed a valley. After the collapse, the working platform at the bottom of the pit was covered by rock and earth, forming a mound 500 meters long, 200 meters wide and 80 meters high.

Rescue teams are carrying out excavation work and searches from both sides of the mound to try and ensure the safety of the trapped workers as well as the rescuers.

The rescue workers are equipped with 14 thermal imaging devices and life detectors to look for survivors' vital signs.

The Ministry of Natural Resources has provided remote-sensing comparison maps to assist the searches. The information is also being used to analyze what caused the accident and how to prevent more occurring.

The ministry has also sent six teams to 12 provincial-level regions to carry out special supervision and inspection of any major hidden dangers in production procedures in the natural resources sector, and improve the methods for exploring and developing mineral resources.