A coach has plunged off a viaduct killing at least 37 people in southern Italy, emergency officials say.

The crash took place near the town of Avellino in Campania region.

The coach, with about 48 people onboard, plunged nearly 30 metres down a steep slope after ramming into several vehicles. The cars hit by the coach piled up on the flyover.

According to local reports, the coach was travelling back to Naples from Telese Terme following a pilgrimage. The highway has been closed following the crash.

The exact cause of the accident is still unclear. The coach was thought be carrying many children. The driver of the vehicle is also believed to have been killed in the accident.

Officials suspect the driver lost control of the vehicle. "I cannot yet confirm the number of victims, we are still pulling people from the vehicle. Our priority now is to free the wounded," a police official told AFP.

Reports suggest nearly a dozen people have been rescued from the coach and admitted to hospital for injuries. Emergency workers are continuing to carry out rescue measures.

"The situation is critical. Our men are working to save as many lives as possible," fireman Pellegrino Iandolo told Italian television channel, SKY TG24.

Local officials are probing the crash.