Coach carrying a group of tourists near town of Avellino careered off a viaduct and plunged down a steep slope

At least 37 people died and many others were injured when a coach carrying a group of tourists through southern Italy crashed into several vehicles, careered off a viaduct and then plunged down a steep slope.

As emergency workers contended with the dark and highly precarious terrain to try to pull bodies from the wreckage, firefighters said most of the bodies had been found inside the coach and a few more beneath the vehicle.

Eleven people – including three children – were injured and taken to hospitals in the surrounding area, the Ansa news agency reported. Two were reported to be in critical condition. State radio quoted Avellino police as saying the bus driver was among the dead.

The wrecked bus lies where it fell after plunging off the road near Avellino. Photograph: Reuters

"The situation is critical. Our men are working to save as many lives as possible," fire chief Pellegrino Iandolo told Sky TG24 television late on Sunday night.

Rescuers wielding electric saws cut through the twisted metal to get to the interior of the bus, stopping occasionally to listen for any cries for help, even as the bodies were put into coffins to be taken to a morgue.

Reports said as many as 49 people had been aboard the bus when it ripped through a guardrail after slamming into several cars, then plunged some 30 metres (100ft) off the highway and into a ravine near a wooded area. The bus tore away whole sections of concrete barriers as well as the guardrail. The concrete lay in large chunks in a clearing where the bus landed.

Coffins are lined up near the crash site. Photograph: Reuters

Television images showed a number of smashed vehicles on the flyover, bodies lying beside the road and the twisted wreckage of the coach lying dozens of metres below the roadside in the undergrowth.

Occupants of cars which were hit by the bus stood on the highway near their vehicles. One car's rear was completely crumpled, while another was smashed on its side. It was not immediately known if anyone in those cars had been injured.

The crash occured about 8.30pm local time between the towns of Baiano Monteforte Irpino, about 40 miles inland from Naples.

Flashing signs had warned of slowed traffic ahead along a stretch of the A16, highway police told state radio early on Monday. They said the bus driver, for reasons not yet determined, appeared to have lost control of his vehicle.

Map showing the crash site. Photograph: Guardian

Reports said it hit several cars and then plunged off the viaduct. There was no obvious cause of the crash, but Ansa reported unnamed sources saying police believed there may have been a problem with the coach's braking mechanism.

A reporter for Naples daily Il Mattino, Giuseppe Crimaldi, told Sky TG24 TV from the scene that some witnesses told him the bus had been going at a "normal" speed on the downhill stretch of the highway when it suddenly veered and started hitting cars. He said some witnesses thought they heard a noise as if the bus had blown a tyre.

Early reports said the passengers had spent the day in Puglia, an area near the Adriatic on the east coast famed for religious shrines. But on Monday, a state radio reporter at the scene said authorities told him the bus had been bringing the passengers home after an outing to a thermal spa area near Benevento, not far from Avellino.

Others at the scene said the passengers might have visited a town near Benevento that was the early home of Padre Pio, a late mystic monk highly popular among Catholics in Italy.

Passengers came from small towns near Naples, and relatives streamed to the crash site. Initial estimates said there were up to 49 people on board at the time of the accident.

A local prosecutor arrived at the crash scene to begin an investigation into the cause of the crash.