PRAGUE, Dec. 21 (Xinhua) -- The death toll of a coal mine explosion near Karvina, Czech Republic, has climbed to 13, of whom 12 are Poles and one is Czech, said OKD mining firm spokesman Ivo Celechovsky on Friday morning.

The seriously injured three, all poles, are staying in hospital, one of them is still in a critical condition, said Celechovsky.

Seven miners with light injuries have been treated by medical staff. Celechovsky said a special commission is investigating the causes of the explosion that happened on Thursday afternoon.

According to OKD director Boleslav Kowalczyk, fire makes the rescue works difficult, OKD tries to block the space to prevent it from spreading. The construction of barriers will last until Sunday.

Of the 13 dead miners, only one body of them has been taken up to the surface so far, the others remain underground, said Celechovsky. It is not yet clear when their remains could be pulled out, but it will be possible after the New Year at the earliest.

The explosion happened at about 880 metres underground and devastated the mining workplace. The CSM nime is a part of the Czech state-owned OKD company. The accident is the second most fatal one in Bohemia and Moravia region in the country since 1990.

Both Czech Prime Minister Andrej Babis, Polish Prime Minister Mateusz Morawiecki went to the scene of the accident. Babis expressed sympathy to the victims' families. Morawiecki described the disaster as a huge tragedy. Polish rescuers will be assisting Czech counterparts when in need.