Published: Apr 12, 2010 4:06 PM EDT

ROME, Italy - A mass of mud and water slammed into a small commuter train traveling in the Italian Alps Monday, knocking the front car into a ditch and killing nine people aboard, officials said.

A Bolzano province official, Francesca De Carlini, said the two-car train, filled with local commuters and students, was passing by at the exact moment that a large irrigation pipe on higher elevation burst. "A mass of mud and water knocked down the first car into the ditch," she said.

"All of the dead were in the first car, which was pulled down into the ditch," De Carlini said by telephone. She discounted earlier media reports of the possibility of three missing, saying the death toll was definitive at nine and that all bodies had been identified.

There were also 28 injured, including seven hospitalized in serious condition, De Carlini said. A geologist was examining the terrain, near the border with Austria, but it was not clear why the pipe burst, she said. A magistrate has begun an investigation into the cause, but the rupture didn't appear to be due to cold weather.

De Carlini said the accident occurred shortly after 9 a.m. and that help arrived within a few minutes. Helicopters, ambulances and firefighters rushed to the scene to rescue survivors. The train had been nearing its destination of Merano, about 300 kilometers (185 miles) north of Venice, after departing from the small town of Malles. The train line runs between the Adige river and mountains. Adige river and mountains.