A statement from OBB, Austria's state railway, said initial investigations show that a supervisor neglected to trip a signal after manually activating a rail switch. The switch usually works automatically and sets off the signal but was stuck due to snow and ice.
The accident occurred with the two trains heading in opposite directions on a single set of tracks. The signal would have normally warned one of them to wait on another set of tracks until the other one passed.
The statement said the accident was apparently due to "human error of the responsible supervisor."
Two helicopters from the Austrian motor club OAMTC joined ambulance crews in evacuating the wagons after the early morning accident.
OBB said final results of the investigation will be published in the coming days.