A landslide swept a passenger train off the rails in mountainous northern Italy on Monday, killing nine people and injuring 28, and leaving one car dangling precariously over the Adige river.

The regional three-carriage train came off the rails at around 9:00 am (0700 GMT) when the landslide hit the front passenger car near the city of Bolzano, a rescue official said.

Seven seriously injured people were hospitalised.

The toll, which was revised down from 11 because of an error, is not final, since "there could still be someone buried in the mud," said Bolzano provincial governor Luis Durnwalder, quoted by the ANSA news agency.

Another train had passed in the other direction without incident just two minutes before the landslide struck in the rugged mountain area, he said.

"The operation posed immediate difficulties given that the first car was dangling between the rails and the Adige River... and the second was invaded by mud and debris," he added.

The front car of the train lodged between two large trees which stopped it from falling into the river below between the towns of Laces and Castelbello.

The wagon was left hanging precariously over the river and firefighters used cables to prevent it from slipping further down the mountainside.

Rescue workers had to climb up from the forested riverbank to reach the train, comprising a passenger carriage at each end and a locomotive in the middle.

The some 400 cubic metres (14,000 cubic feet) of mud covered around 15 metres (50 feet) of track, according to a local geologist, Ludwig Noessing.

A field hospital was set up nearby, media reports said.

"We are speechless over this catastrophe, whose magnitude and causes are not completely clear yet," the head of the Bolzano provincial council, Dieter Steger, said in a statement.

Consumer advocacy group Codacons, calling the accident "a massacre of innocents," demanded an investigation into any "omissions or neglect on safety or maintenance over the entire rail line."

Police have located the train's badly damaged "black box," reports said.

According to a preliminary reconstruction, the landslide was caused by a broken irrigation pipe in a field above the rails, "drenching the terrain below," a provincial spokesman told Italian television.

The railway line, inaugurated in 2005, is considered one of the most modern in the country.

Italian Transport Minister Altero Matteoli expressed "condolences to the victims families", but refused to make any "hypothesis about responsibilities for the cause."

Prosecutors in Bolzano have opened an investigation.

Monday's accident was the worst in Europe since a Belgian train crash in February in which 18 people died when two rush-hour commuter trains collided outside Brussels.

Italy suffered its worst rail accident in 20 years last June, when 29 people died after a freight train ferrying liquefied petroleum gas derailed in Viareggio, on Italy's northwest coast, causing a series of explosions.

The force of the blast brought down two small blocks of flats, where many of the victims lived.