Polish rescue workers have pulled another victim from the wreckage of a head-on collision between two passenger trains, raising the death toll to 16.

Rescuers worked through the night to pull survivors and recover bodies from the site of the crash, which took place late Saturday. At least 56 of the estimated 350 people on board were injured, including some in serious condition.

The impact left tons of mangled metal on the tracks, with train cars overturned and piled on top of each other.

Prime Minister Donald Tusk called the accident “the most tragic train catastrophe” in Poland in recent years, after visiting the site early Sunday. President Bronislaw Komorowski said he would announce a period of national mourning.

Authorities say the trains were traveling toward each other on the same track when they crashed in Szczekociny in southern Poland. One train was en route to the capital, Warsaw, from the southeastern city of Przemysl, while the other was heading south from Warsaw to the city of Krakow.

Officials are investigating to determine how one train ended up on the wrong track.