"We can confirm six people have died. It's difficult to give an accurate toll," he said.
Local police told AFP that about fifty people had been injured in the crash. Polish media reports spoke of sixty injured, including thirty seriously.
The collision took place at 9:00 pm (2000 GMT) between two trains travelling on the same track, a Polish railways official said. One was en route to the southern city of Krakow from the capital Warsaw, while the other was travelling to the capital from the south-eastern city of Przemysl.
Initial images of the crash broadcast by the TVN24 commercial news channel showed mangled wreckage.
One survivor told the channel they had seen dead bodies as well as people still alive but pinned down inside the train wrecks.
Injured survivors were being evacuated to hospitals in the region. Firemen were trying to reach those still inside the wreckage in the early hours of Sunday.
"We are trying to reach several people inside the wagons with whom we have established contact," Jaroslaw Wojtasik, a fireman on the scene told TVN24.
Poland's Prime Minister Donald Tusk, Transport Minister Slawomir Nowak as well as the interior minister were travelling to the site of the accident late Saturday night, according to a government statement.