President Xi Jinping has sent a message to his Russian counterpart Vladimir Putin to express his condolences after a major coal mine accident in Russia's Kemerovo Region in western Siberia.

Fifty-two people were killed following a gas explosion in the Listvyazhnaya mine on Thursday. It was the deadliest mine accident in five years in the country.

In the message, Xi said he was shocked upon hearing of the accident.

On behalf of the Chinese government and the Chinese people, and also in his own name, Xi said he deeply mourns those killed in the accident and expressed sympathy to the bereaved families and those injured.

On Thursday morning, authorities received reports of smoke from the mine, and rescuers and medics were sent to the site.

According to the Ministry of Emergency Situations, there were 287 miners in the mine at the time of the incident. A total of 239 people have so far been evacuated.

Russian news agencies quoted local authorities as saying that 52 people were determined to have died at the mine since Thursday, including miners and six rescuers.

"According to preliminary information, no one is still alive in the mine," TASS news agency quoted a local emergency services source as saying.

Search-and-rescue efforts for the trapped miners were suspended due to high methane concentrations and the risk of further explosions.

A team of six rescuers who were sent to find the trapped miners stopped responding to communications, the ministry said, and Interfax quoted a local official as saying they had suffocated.

According to regional authorities, 38 miners have been hospitalized with injuries. RIA Novosti reported that three of those hospitalized are in critical condition.

A local rescue squad commander said miners and rescuers were unable to survive due to a lack of oxygen and a high concentration of gases.

"It was a tragedy yesterday. It is impossible to speak about anyone's survival in the atmosphere that is currently present at the emergency area," the commander said, adding that carbon monoxide, which can be absorbed through the skin, is extremely dangerous for people in the mine.

Deputy Prosecutor General Dmitry Demeshin was quoted as saying that the incident was the result of a methane explosion caused by a spark.

But some Russian media reported that dust in a ventilation shaft caught fire, causing the mine to fill with smoke.

The region's governor declared a three-day mourning period beginning on Friday.