Polish emergency officials say two passenger trains have collided head-on, killing 15 people and injuring at least 54.

Prime Minister Donald Tusk called the accident “the most tragic train catastrophe” in Poland in recent years, after visiting the site early Sunday.

Authorities say the trains were traveling toward each other on the same track late Saturday when they crashed in Szczekociny in southern Poland. Officials are investigating to determine how one train ended up on the wrong track.