Croatian police said on Thursday they seriously wounded two 12-year-old migrants from Iraq and Afghanistan after opening fire on a van which refused to stop.

The shooting occurred late on Wednesday night when the vehicle illegally crossed the border from Bosnia, spokesman Elis Zodan told AFP.

Police opened fire and then discovered 29 illegal migrants in the van, including the two children, who were hospitalised and are now in a stable condition, he said.

The driver of the van, that had Austrian registration plates, fled into the woods and police were searching for him, Zodan added.

Police said they twice tried to halt the van but the driver "charged the vehicle at police ... after which they opened fire," according to the spokesman.