The accident happened at Meidling station, near the center of the Austrian capital, on Saturday afternoon. A Railjet intercity train headed for Villach in southern Austria with 30 people on board hit an empty regional train.
It wasn't immediately clear what caused the accident, which resulted in part of the Railjet train derailing and tipping over.
Nine people were hurt, though the most severe injury was a hand fracture, the Austria Press Agency reported.
Roman Hahslinger, a spokesman for railway company OeBB, said that a technical problem and human error were both possible causes. Investigators planned to question both train drivers, neither of whom was injured, as well as dispatchers.