A methane gas blast ripped through the Raspadskaya mine on Saturday night, followed hours later by a stronger explosion that wrecked the main ventilation shaft and badly damaged buildings on the surface.
"Search operations have been halted," Emergencies Ministry official Pavel Plat said.
Fires burning in the mine and high levels of methane gas could lead to new explosions, he said in a statement.
"Our task is to put out the fires and decrease the gas concentrations - only after that can we send people in there," Plat said. "Unfortunately, conditions have worsened."
The bodies of six miners were brought to the surface overnight, taking the confirmed death toll to 66, the ministry said. It said 24 miners were missing.
The disaster at the mine in the city of Mezhdurechensk, 3,000 km east of Moscow, was the deadliest in a Russian mine since 110 people were killed by a methane blast at another mine in the coal-rich Kemerovo region in March 2007.
