At least 24 people, most of them teenagers, have been killed in a road crash in northern Spain.

About 30 others were injured, some of them seriously, when a bus carrying schoolchildren collided with a lorry.

The bus and the lorry transporting pigs are believed to have collided head-on, as they drove along the N-122 highway linking Zaragoza with the Portuguese border.

The impact sent the bus plunging down an embankment. The driver is believed to be among the dead.

Rescue officials said the death toll could rise further, as a search of the wreckage was continuing.

The teenagers were said to be from two schools in Barcelona and heading for a holiday camp near Soria, northeast of Madrid.

The crash happened near the village of Golmayo, several kilometres from Soria.

"We don't have too many details but most of the victims are about 14 years old," a hospital spokesman in Soria said.

He said a team of psychologists was being brought in to help family members and survivors cope with the trauma.

State radio reported that relatives of the victims headed to the site, where at least three fainted and were taken away in ambulances.

Pigs which escaped from the overturned truck were later running loose in nearby fields.