The accident happened near the city of Merano, about 300 kilometers (185 miles) north of Venice.
The Carabinieri police in the nearby town of Silandro said seven people were killed and about 25 were injured. The ANSA news agency said some were in serious condition and had been taken to hospitals.
The train line runs between the Adige river and mountains on the other.
Thomas Widmann, a transport official in Bolzano, the biggest city nearby, said the landslide was caused by an irrigation pipe that burst open, sending rocks, debris and water down onto the oncoming train at around at 9:30 a.m.
Officials said it was a small, local train. It was not clear how many passengers were on board.
At least one carriage was destroyed, its windows shattered, ANSA said. The carriage was prevented by trees from plunging into the river.
