A dog sled race considered one of the toughest on the European continent is under way in the northeastern Czech Republic.

Almost 100 mushers from eight countries with some 500 dogs are competing in the Sedivackuv Long. They have to overcome 240 kilometers (149 miles) in deep snow and freezing condition in the Orlicke mountains located on the Polish border in four days. Competitors also have to spend one night sleeping in the snow.

The 16th edition of the race will be completed on Saturday. It is part of the European extreme dog sled race series.

Race organizer Pavel Kucera said Thursday: "It is one of the longest races and with it's difficulties it belongs to some of the toughest races in Europe apart from the Nordic countries where the conditions are little different."