TEMPE, Greece — A passenger train in Greece carrying hundreds of people collided with an oncoming freight train in a fiery wreck in the country’s north early Wednesday, killing 29 and injuring at least 85, officials said.

Multiple cars derailed and at least three burst into flames after the collision near Tempe, a small town next to a valley where major highway and rail tunnels are located, some 235 miles north of Athens.

Survivors said several passengers were thrown through the windows of the train cars due to the impact. They said others fought to free themselves after the passenger train buckled, slamming into a field next to the tracks.

Hospital officials in the nearby city of Larissa said at least 25 people had serious injuries.

“The evacuation process is ongoing and is being carried out under very difficult conditions due to the severity of the collision between the two trains,” said Vassilis Varthakoyiannis, a spokesperson for Greece’s firefighting service.

Rescuers wearing headlamps worked in thick smoke, pulling pieces of mangled metal from the cars to search for trapped people. Others scoured the field with flashlights and checked underneath the wreckage. Several of the dead are believed to have been found in the restaurant area near the front of the passenger train.

The possible cause of the collision was not immediately clear. Two rail officials were being questioned by police but had not been detained.

Passengers who received minor injuries or were unharmed were transported by bus to Thessaloniki, 80 miles to the north. Police took their names as they arrived, in an effort to track anyone who may be missing.

A teenage survivor who did not give his name told reporters as he got off one of the buses that just before the crash, he felt a strong braking and saw sparks and then there was a sudden stop.

“Our carriage didn’t derail, but the ones in front did and were smashed,” he said, visibly shaken.

He added that the first car caught fire and that he used a bag to break the window of his car, the fourth, and escape.

Rail operator Hellenic Train said the northbound passenger train from Athens to Thessaloniki, Greece’s second-largest city, had about 350 passengers on board.

In comments to state television, Costas Agorastos, the regional governor of the Thessaly area, described the collision as “very powerful” and said it was “a terrible night.”

“The front section of the train was smashed. … We’re getting cranes to come in and special lifting equipment clear the debris and lift the rail cars. There’s debris flung all around the crash site.”

Officials said the army had been contacted to assist.

Hellenic Train, which has added highspeed services in recent years, is operated by Italy’s FS Group, which runs rail services in several European countries.

Gatopoulos reported from Athens.