A gas explosion at a Siberian colliery on Saturday killed 20 miners and rescue teams combed a vast shaft for 25 others missing underground, officials in the region said.
A spokesman for Siberia's Kemerovo district - heart of the Kuzbass coalfield where accidents are a regular occurrence - said rescuers had brought 20 bodies to the surface more than 12 hours after the accident.
"There was a big explosion and then a serious collapse of the shaft's walls. Both the electrical and ventilation systems failed," Sergei Cheremnov said by telephone.
"We are still looking for 25 miners."
Six miners scrambled out of the Taizhina mine in the town of Osinniki after the gas leak occurred at about 6.30 am. Three were pulled free with serious burns.
The missing miners were believed to be trapped 700 metres (2,200 feet) below the surface. No contact had been established with them, officials said.
A local official had earlier said the accident was caused by "a release of methane".
Kemerovo's high-profile governor Aman Tuleyev, shown on television co-ordinating rescue efforts, said teams were making their way towards the trapped miners by both a direct route and a five km (three miles) detour through a nearby mineshaft.
Television showed dejected miners outside the main shaft who had been due to take over on the morning shift. Distraught relatives waited for news in an auditorium.
Russia's coal mines are plagued by accidents generally blamed on lax operating procedures and old equipment.