MOSCOW — Fifty-one people have been killed in Russia's worst mining disaster in a decade, prompting three days of mourning in Siberia's Kemerovo region, BBC reported.

Among the dead were five rescue workers, although a sixth was found alive and taken to hospital in a serious condition.

Acting Emergencies Minister Alexander Chupriyan said the man found in the mine was a rescuer who had been presumed dead.

The blast happened at the Listvyazhnaya mine when coal dust caught fire in a ventilation shaft on Thursday.

Rescuers suffocated as they tried to reach dozens of missing miners.

At the time of the accident early on Thursday there were 287 people in the mine, some 3,500km (2,175 miles) east of Moscow.

Many managed to get out and 49 people were taken to hospital, some of them suffering from smoke inhalation.

But dozens were trapped and rescue operations had to be suspended because of high concentrations of methane.

Officials said a methane gas explosion had filled the mine with smoke and the victims had died because of a lack of oxygen and high concentration of poisonous gas.

The survivor from the rescue team was named as Alexander Zakovryashin and Chupriyan said it was a "miracle carried out by our people".

Russian mine accidents are not uncommon and this is not the first accident at Listvyazhnaya. In 2004, a methane gas explosion left 13 people dead.

In 2016, authorities assessed the safety of the country's 58 coal mines and declared 34% of them potentially unsafe. The list did not include the Listvyazhnaya mine at the time, reports say.

President Vladimir Putin described the loss of life as "a great tragedy".

The state Tass and RIA-Novosti news agencies on Thursday had cited emergency officials as saying that there was no chance of finding any more survivors, and put the death toll at 52 on Thursday evening. Rescuing a survivor on Friday morning brings that down to 51.

Regional officials declared three days of mourning. Russia’s Investigative Committee has launched a criminal probe into the fire over violations of safety regulations that led to deaths. It said the mine director and two senior managers were detained.

One more criminal probe was launched Friday into the alleged negligence of state officials that inspected the mine earlier this month. — Agencies