Rescuers battled smoke and blistering temperatures on Friday to reach 31 miners trapped underground for nearly a day by a fire at a gold mine in Eastern Siberia.
Working through the night, rescuers tried to put out the blaze and bring the men to the surface through tunnels. One team of rescuers was forced to return to the surface because of thick smoke and high temperatures.
The fire was sparked on Thursday at 2:15pm by welding work deep in the central shaft of the Darasun mining complex, owned by Highland Gold, in Russia's remote Chita region on the Chinese border.
Sixty-four miners were below ground when the fire broke out and some managed to crawl to safety through a tunnel. But the condition of the 31 trapped miners was unclear as rescuers said they had no way of communicating with them.
"The rescue operation is continuing and has gone on through the night," an official at the Emergencies Ministry in Chita, 5,000 kilometres east of Moscow, said.
"We do not have any contact with the people trapped below. We are striving to get them out."
The official said the fire, which broke out at a depth of between 85 and 135 metres, had been isolated but not put out.
A team of 18 rescuers were forced to come to the surface because of high temperatures and thick smoke, the local official at the scene told Interfax news agency.
Rescue teams were being drafted in from neighbouring cities to help the operation as emergency workers tried to bring the miners to the surface through a horizontal tunnel linked to a second vertical shaft, five kilometres from the blaze.
"The rescuers are continuing their work and are working through the night," a Highland Gold spokesman said. "The main thing is to rescue the people trapped below."
Russia's gold mines have a generally better safety record than the more hazardous coal mining industry, which has been plagued by fatal accidents since the collapse of the Soviet Union in 1991.
Underinvestment, low pay and sloppy safety standards have been blamed for a series of mining disasters, the most recent of which was a blast at a Siberian coal mine in 2005 in which more than 20 died.
Russia's environmental watchdog said it would probe all Highland Gold's activities, including those in other regions.
"We have repeatedly made geological checks, have found violations everywhere, have given instructions, but the bulk of them have never been implemented," it said in a statement.
Highland Gold's shares fell by 4.5% in London on Thursday after news of the fire.
The Darasun mine, the smaller of Highland Gold's two main gold projects in Russia, produced 11,761 ounces of gold in the first half of this year, or around 13% of the company's total production.
Highland Gold has forecast total gold output this year of 180,000 to 185,000 ounces.
The company is one-fifth owned by Canada's Barrick Gold, the world's largest gold miner.