Serbian authorities say two migrants are dead and two others are in serious condition after hiding in a truck tank in a bid to reach Western Europe.

The men were discovered two days ago in northern Serbia when the truck driver opened the tank for washing and saw them lying unconscious.

The Clinical Center of Vojvodina on Thursday said the migrants suffered from hyperthermia and hypoxia. One died on Wednesday and the other died overnight. The two others are in intensive care.

Police say at least two of the migrants are from Afghanistan.

Thousands of migrants fleeing war and poverty have been moving through the Balkans in a bid to reach wealthy nations in the West.