Emergency teams in southern Russia have spent the night digging a tunnel to free 13 coal miners trapped underground but hopes for their survival are fading as water keeps gushing into the mine.
That followed a day of euphoria on Saturday when rescue workers brought out 33 of the 46 miners who were trapped in the flooded mine shaft, a rare streak of luck for Russia's antiquated coal industry plagued by a disastrous safety record.
The fate of the remaining 13 miners remained unknown.
"Thirteen is an ominous number," a senior Emergencies Ministry official, who asked not be named, told Reuters outside the mine's main entrance.
"A lack of oxygen is the biggest problem. On top of that we have water keeping pouring into the mine," the official said.
Emergency teams first rushed to the Zapadnaya-Kapitalnaya mine in Russia's Rostov region on Friday when an underground lake burst open, inundating the mine and knocking out power.
Miners trapped inside split into two groups, the larger managing to find a way towards a remote secondary shaft, from which they were pulled to the surface.
The smaller group is believed to be stuck in an elevated part of the mine, surrounded by rising floodwater. There is no contact with them though some of the rescued miners said they communicated with their 13 colleagues shortly after the accident.
Attempts to stem the water flow by hauling thousands of tonnes of rocks into the main shaft have failed.
"We could not block the shaft, water is pouring in at the same rate as before," the Emergencies Ministry official said.
The fate of the trapped miners now depends on a rescue team burrowing a tunnel towards them from a neighbouring mine. But progress appeared to be slow as using machinery was impossible and all work was done by hand.
Viktor Kapkanshchikov, the Emergencies Ministry rescue operations chief, said rescuers expected the tunnel to reach the flooded mine on Tuesday but might not meet the deadline.
"We will dig for as long as it takes, until we get there," he said.
Interfax news agency quoted a member of the crisis team, Sergei Mikhalyov, as saying that with water arriving at the current rate the mine would be fully flooded within the next 40 hours. To avoid that rescuers would try to pump out water through a ventilation shaft, he said.