At least 13 coal miners have been killed in the Czech Republic following a deadly methane explosion around 2,600 feet underground.

The level of methane in the mine near the town of Karvina was at least 4.5 times the allowed level at the time of the explosion Thursday afternoon, said Bohuslav Machek, a spokesman for the Czech mining authority.

"To our knowledge... there is a fire underground, very high temperature, very high risk of subsequent explosions," Polish Prime Minister Mateusz Morawiecki added.

CLICK HERE TO GET THE FOX NEWS APP

Officials say 12 of the dead were Polish nationals while one was Czech, and that 10 other miners were injured in the blast. Rescuers are braving the fire in an attempt to recover the bodies.

Polish President Andrzej Duda declared Sunday a day of national mourning for the victims of the tragedy. Flags in Poland will be lowered to half-staff on public buildings and large sporting and entertainment events will be canceled.

WEST VIRGINIA MINE RESCUE SPURS CONCERNS OVER COPPER THEFTS

Morawiecki and his Czech counterpart Andrej Babis have offered their condolences to the families of the victims. The two leaders visited the mine on Friday.

One of the miners injured in the explosion was in critical condition with burns over 50 percent of his body, a hospital spokesperson told the Associated Press.

13 YOUNG MINERS FEARED DEAD IN INDIA

"I wish to express words of deepest sympathy to all the close victims of the mining disaster in Karvina," Morawiecki said. "This is a huge tragedy for all Poles and Czechs. On this difficult day, we strongly show our solidarity and sense of national community."

Czech officials say efforts to recover the bodies are ongoing Friday despite a fire in the mine.

The Associated Press contributed to this report.