A gas explosion on Tuesday in a coal mine in Poland killed at least eight miners, the president of the company that owns the Halemba mine said.
"Four bodies have already been brought to the surface," said Grzegorz Pawlaszek of the situation at the mine in Ruda Slaska, which lies near the city of Katowice in Poland's southern Silesia coalbelt.
More than a dozen miners remain trapped underground while rescue efforts are under way in "extremely difficult conditions", according to Zbigniew Madej, a spokesman for the mining company.
"It is impossible to breathe in the area of the explosion, the ventilation has been destroyed, which is very disturbing information," he added.
The blast, which occurred on Tuesday afternoon some 1,000 meters (3,000 feet) below the surface, cut off all communication with the miners, said Jan Sienkiewicz, a spokesman for the mining company.
Polish Prime Minister Jaroslaw Kaczynski has arrived at the mining site, along with the ministers for transportation and the economy.
"We must still hold onto hope, but if the worst has happened, the families of the miners will receive the necessary aid," Kaczynski said.
"The death of eight miners is already a great tragedy," he said, adding that a national mourning will be decreed in Poland.
It was the second accident in four months to hit the small mining community of Ruda Slaska. Four miners were killed there in July when a shaft caved in at another mine in the town.
Mining accidents have claimed the lives of 13 miners in Poland so far this year, and around 20 last year.