A passenger train has derailed in Poland, killing four people and injuring at least 20 others.

The train was traveling between Warsaw and Katowice when it derailed near the town of Baby, with the engine and three cars leaving the tracks, and at least one car tipping over on its side.

The cause of the accident was not immediately known.

Rescue teams said the injured were transported to local hospitals. Emergency officials are concerned there may be more injuries because some passengers were thrown through windows and could be pinned under the overturned rail cars.

Passengers reported hearing a loud noise before the accident.