The scene outside the mine
At least 12 miners have been killed and 83 others are trapped following two explosions at Russia's largest underground coal mine.
Twenty of those still in the Raspadskaya mine, in western Siberia, are rescuers sent in following the first blast, officials say.
The country's emergencies minister said 55 miners have been injured.
Many of Russia's mines have poor safety records, and there have been calls for standards to be tightened.
More than 300 were underground when the first explosion happened just before midnight on Saturday and most were brought safely to the surface. Reports blamed the blast on methane gas.
Officials said 12 miners died in the first explosion. The second explosion came about three hours later and contact with a team of 20 rescuers was lost.
Emergencies minister Sergei Shoigu said 12 miners were killed in the blasts and 55 wounded, the Interfax news agency said.
Rescue efforts were suspended, although were due to resume on Sunday evening, a rescuer told Itar-Tass news agency.
"The mine is being ventilated to reduce the concentration of gas. There is no contact with the workers inside the mine," he was quoted as saying.
The governor of Siberia's western Kemerovo region, Aman Tuleyev, has taken charge of the rescue operation.
He said the second blast had destroyed the main air shaft, causing more injuries, and there was a risk of more explosions.
"The rescue work will continue when the atmosphere in the mine is restored, but to conduct rescue work now means to send people to their death," he said.
Emergency teams are now trying to pump air into the underground shafts.
Vladimir Putin said the rescue operation should resume as soon as possible.
Speaking at a meeting with emergency officials broadcast on state TV, the Russian Prime Minister said: "It is clear that the situation at the mine is very hard. I would say that it is tragic.
"The saddest thing is that we cannot send in additional rescuers now as it is very dangerous due to the lack of ventilation.
"But we cannot sit on our hands and must do everything to save people," he was quoted as saying by AFP.
State TV pictures showed that the explosions had been so powerful that buildings on the surface had been badly damaged.
The mine, about 3,500km (1,900 miles) east of Moscow, produces about eight million tons of coal a year, according to its website.
Kemerovo is part of the major coal-producing Kuzbass region.