Workers in southern Poland have been bringing heavy equipment to the scene of a head-on train collision that killed 16 people and injured 56 others in the country's worst rail disaster in more than 20 years.

The two express trains, carrying an estimated 350 passengers in 10 carriages, were heading in opposite directions on the same track when they crashed at high speed in a rural area near the small town of Szczekociny on Saturday night.

Andrzej Pawlowski, a member of the board of the state railway company PKP, said one of the trains, which was travelling south from Warsaw to Krakow, should not have been on the track.

Eyewitness accounts

A woman living in a house 200 metres from the scene said she was standing at her window when the trains collided, creating a "terrible, terrible noise — like a bomb going off."

"So I ran out of the house, and on one side I saw train lights and one the other side I saw train lights, and in the middle sparks," Anna Sap said. "People from the train starting crying, 'Help, help!' So we and the neighbours ran to them. Some of them smashed windows to let them out."

Her husband Grzegorz Sap said people began emerging from the train "with hand luggage and in shock. They had no idea where they were."

An unnamed passenger interviewed on the all-news station TVN24 said he felt the force of the collision.

"I hit the person in front of me. The lights went out. Everything flew," he said. "We flew over the compartment like bags. We could hear screams. We prayed."

-Associated Press

The other train, headed from the eastern city of Przemysl to Warsaw, was on the correct track, Pawlowski said.

It wasn't immediately clear how the southbound train ended up on the wrong track. Maintenance work was being carried out on one of the tracks where the collision occurred, around 9:15 p.m.

On Sunday, Poland's president Bronislaw Komorowski visited a hospital where several of the wounded were admitted and met briefly with hospital staff. Earlier in the day, he visited the crash site and said when rescue efforts are over he would make an announcement about a period of national mourning.

"The scale of this phenomenon is so large that there should be nationwide mourning," Komorowski said.

A spokesman for the U.S. consulate in Krakow, Benjamin Ousley, said an American woman was among those who died. He did not give additional  information. Polish authorities have yet to release any information about the victims.

One of the locomotives ended up on top of a carriage that lay flattened underneath. Many of the derailed cars were buckled and torn apart from the impact. One car had jack-knifed upwards from the force of the crash while others had derailed and were lying on their sides.

"This is our most tragic train disaster in many, many years," Prime Minister Donald Tusk said.

Crews were trying to free a body from the mangled wreckage of the train Sunday morning, while the injured were being treated in several area hospitals.

A doctor in one area hospital, Szymon Nowak, said many of the injured were in a serious condition, with some in artificially induced comas.

With files from The Associated Press