Two trains have collided in southern Poland, leaving 14 people dead, local officials say, and 50 hurt.
The accident occurred on Saturday evening on the Warsaw-Krakow mainline at the small town of Szczekociny, according to Polish TV.
Two express trains, one of which was on the wrong track, collided head-on, a senior railway official said.
Prime Minister Donald Tusk arrived at the scene early on Sunday morning, with three other cabinet ministers.
"This appears to be one of the most serious railway accidents in recent years," Transport Minister Slawomir Nowak told the TVN24 news channel.
Some passengers remain trapped in the wreckage, police say. Helicopter ambulances from Warsaw and Wroclaw are helping to take the injured to hospitals.
"The rescue is difficult and complicated," firefighter Jaroslaw Wojtasik told Polish television.
"The damage to the wagons is huge. We have contact with victims. We are approaching very cautiously."
The accident occurred at 21:15 (20:15 GMT), when a train travelling north from Przemysl to Warsaw collided with a southbound train from Warsaw to Krakow.
Scheduled engineering works were taking place on one track at Szczekociny station at the time of the accident.
The Krakow train was on the wrong track, Andrzej Pawlowski, a member of the board of the state railway company PKP, told the TV station TVN24.
Three coaches are reported to be especially damaged, and the rescue operation is focusing on finding passengers there.
The three coaches were "completely destroyed - like a concertina", one eyewitness told the Gazeta Wyborcza newspaper.
Another passenger estimated that his train was travelling about 120km/h (75 mph), when it started braking very sharply.
"Then we felt a powerful impact, and we were thrown about the compartment," the passenger told TVN24.