Italy bus crash
a bus ripped through a guardrail and plunged off a viaduct near the southern Italian town of Avellino (Reuters)

A bus crash that killed at least 38 people and injured 10 in southern Italy was triggered by a tyre blowout, a survivor has claimed.

The bus carrying as many as 48 people ripped through a guard rail and plunged some 30 metres (100 feet) off a viaduct after it lost control near the town of Monteforte Irpino, about 40 miles (60km) inland from Naples.

"My niece said the left tyre exploded. The driver tried everything to keep the bus on track but unsuccessfully. It swerved and fell into the ravine." Vincenzo Rusciano told reporters after visiting his niece, Annalisa, at a local hospital.

Annalisa, her husband and their two children all survived the incident and are recovering from the injuries suffered at three separate hospitals. Another four of Rusciano's relatives died in the crash.

The passengers were a group of families and friends that often went for weekend trips altogether, Italian news agency Ansa reported.

They were on their way back to Naples at the end of a two-day journey to Telese Terme and Pietralcina, the early home of Padre Pio, a mystic monk hugely popular among Catholics in Italy.

Six children were on board as the bus rammed into several vehicles that were left smashed on the flyover, before plummeting from the viaduct.

They all survived and were rushed to local hospitals, where two are reportedly in serious condition.

Authorities are probing the incident and assessing whether the bus had faulty brakes, as it appears they were not activated by the driver, who died in the crash.

Some eyewitnesses told rescuers that the bus had been going at a "normal" speed on the downhill stretch of the highway but then abruptly steered right to avoid a traffic jam ahead.

"It's a very sad day," commented Italian PM Enrico Letta. "I'm speechless."