A Polish bus carrying Russian youngsters crashed through guardrails and ended up on its side under an elevated highway near the port city of Antwerp on Sunday, killing at least five people and leaving five more critically injured, an official said.

The accident in Ranst happened at dawn and no other vehicles were involved at first sight, said mayor Lode Hofmans.

"We have five dead and five who are in critical condition," Hofmans said in a telephone interview with The Associated Press. He added two more were seriously injured while seven more had light injuries.

Hofmans said the Polish bus was taking Russian youngsters from Volgograd and was heading towards Paris when the accident happened. He said 42 people were in the bus at the time of the accident, mainly teenagers and a few in their early twenties.

Pictures of the crash scene showed the white bus lying on its side with belongings of the passengers strewn outside. At the crash scene, a crane was trying to lift the bus.