At least four people were killed and 20 others injured in a bus crash in the town of Aviles, northern Spain, on Monday, emergency services informed.

The accident happened when the bus, operated by the company Alsa, was involved in a head-on collision with a viaduct at around 13:40 local time, according to local media reports.

A spokesperson for the Civil Guard reported "a bus came off the road on the way to the airport (Asturias Airport) and collided with a pillar of a section of the new motorway which is currently being built".

The cause of the accident is so far unknown.

Ambulances, Fire-Brigade and Civil Guards are at the scene, A helicopter is being used to ferry the injured to hospitals in the area.