The carriage was left hanging precariously over the river and firefighters used cables to prevent it from slipping further down the mountainside, the ANSA news agency said.
The railway line in the province of Bolzano, inaugurated in 2005, is considered one of the most modern tracks in the country.
Thomas Widmann, a transport adviser to the local provincial government, told Sky Italia television that the landslide appeared to have been caused by
a burst irrigation pipe.
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, with 29 people killed when a freight train ferrying liquefied petroleum gas derailed in Viareggio, on Italy's north-west coast, causing a series of explosions.