Fear of a second gas explosion was slowing efforts to find 15 coal miners missing 1km underground after a blast that killed at least eight miners.
The accident happened on Tuesday afternoon as the men, aged between 21 and 59, were retrieving equipment from a dangerous section of the Halemba mine in the southern city of Ruda Slaska.
Grzegorz Pawlaszek, head of the state-owned Coal Co, said rescue teams had recovered seven bodies from the scene of the blast. Another body had been located but could not be reached because the high concentration of methane gas meant there was the risk of another explosion.
He said the fate of the other 15 was not known. Locator devices carried by the missing miners were emitting no signals.
Still, "there is a chance to find someone still alive," Palwaszek said.
He said rescuers were monitoring the concentration of gas seeping out of the rock before deciding whether to move further ahead through the rubble-filled tunnels.
Early yesterday morning, company spokesman Zbigniew Madej said officials had decided to install ventilator dams to try to lower methane levels in the shaft and allow rescuers to push ahead.
The affected shaft was closed in March because high gas concentrations made further work there too dangerous, Pawlaszek said. However, equipment worth 70 million zlotys (US$23.7 million) was left behind.
"It was new equipment and that is why we decided to retrieve it," Pawlaszek said, adding the work was done under increased security and under the supervision of specialists in detecting gas.
He said the recovered bodies had burns and were hard to identify because ID tags were torn away in the blast.
Earlier, Madej said 15 rescue workers were digging their way through 500m of rubble in the hope of finding survivors but said ventilation systems had been damaged.
Inside the mine complex, officials and priests were counseling distraught relatives seeking word on missing loved ones.
Miners leaving the premises early yesterday after completing their shifts in parts of the mine still operating were downcast.
"There is fear," said Krzysztof Przybyla, a 34-year-old who knew some of those trapped. "This could have happened to any of us."
Labor unions complain that a lack of investment and massive layoffs in recent years have resulted in falling safety standards at the nation's mines.
The Halemba mine, located in the heart of the Silesia industrial region, opened in 1957 -- making it one of the oldest -- and has a record of serious accidents.
In 1990, 19 miners were killed and 20 injured in a gas explosion there and a 1991 cave-in killed five more. Earlier this year, a Halemba miner was rescued after he spent five days underground following a gas explosion.