At least 14 people have died and many are injured or stuck after a fire broke out in a coal mine in the Kemerovo area of Siberia, Russian authorities said on Thursday.
Eleven of the dead are miners, while three people are rescue workers who died trying to help the injured.
"35 people are underground, we know who they are but we have not been able to determine exactly where they are," Governor Sergei Tsivilev said in a statement broadcast by a local television channel.
In total, the death toll could move up to 50 dead, several news media report.
Rescue work was stopped
The rescue work had to be interrupted due to the risk of explosion in the afternoon.
According to Russian media, almost 300 people were in the mine 250 meters underground.
Cold dust caught fire, which caused smoke to spread quickly via the ventilation system, says a source to the news agency Tass.
Russia has launched a criminal investigation to see if security has been breached.
According to the Russian commission of inquiry, the director of mining and two senior executives have been arrested.
President Vladimir Putin has expressed his condolences to the families of the dead and ordered the government to offer all necessary assistance to the injured.
In 2016, 36 miners were killed in a series of methane explosions in a coal mine in northern Russia.
Following the incident, Russian authorities reviewed the safety of the country's 58 coal mines and declared 20 of them potentially unsafe.