Russia's largest coal mine has been hit by a second explosion hours after a deadly methane blast killed at least 12 workers and left scores of others trapped underground.
Al Jazeera's Neave Barker said that the second blast on Sunday forced rescue operations to be halted due to fears of further blasts.
"Rescue operations will resume once the safety situation has improved and the gas in the mine shaft disperses," Barker said.
He said that over 80 miners and rescuers are trapped underground following the second blast and there had been no radio contact with the rescuers since then.
"It is clear that the situation at the mine is very hard. I would say that it is tragic," Vladimir Putin, the Russian prime minister, said.
"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," Putin said.
The second blast damaged a ventilation shaft and choked the mine with smoke and gas.
The first blast late on Saturday, while 370 people were working in the mine, killed 12 workers and injured 55, Sergei Shoigu, the emergencies minister, said.
The first explosion at the Raspadskaya mine in the Kemerovo region of Siberia - the country's largest coal mine - was caused by methane gas but the authorities did not specify what caused the second blast.
"Basic safety regulations were not upheld or not in place at all," Barker said.
"Officials say that a criminal investigation for negligence of security rules in mining is now under way."
The Raspadskaya mine produces about 8 million tonnes of coal a year, according to the company's website.
Mine explosions and other industrial accidents are common in Russia and other former Soviet republics, and are often blamed on inadequate implementation of safety precautions by companies or by workers.
In December, nine people were killed in an explosion at an iron-ore mine in the Urals Mountains region that was blamed on faulty transportation of explosives.
In 2007, a blast at the Ulankovskaya coal mine, also in Kemerovo, left more than 100 people dead.
The authorities had announced in the aftermath of that blast that all surrounding mines would be checked for safety.