When the passenger train from Athens slammed head-on into a freight train from Thessaloniki late on Tuesday night, 22-year-old Angelos was in the penultimate carriage.

Still, "it felt like an earthquake," he told AFP.

The passenger train's two front carriages were crushed in the collision while the third carriage -- the restaurant car -- vaulted over them and caught fire.

"I saw scenes of horror in the first carriages. I'm still shaking," Angelos said.

Surrounded by swirling smoke and the sight of the wreckage, rescuers stood stunned as the sun rose over the field near the central city of Larissa where the crash took place.

Police and emergency crews search wreckage after the train accident. Photo: AFP

The fire department later said temperatures in the restaurant car hit 1,300 degrees Celsius (2,370 degrees Fahrenheit).

"It's like a warzone, and maybe the word doesn't fully reflect conditions," Larissa Mayor Apostolos Kalogiannis, told Skai TV.

"Unfortunately, some of these people will only be able to be identified" via DNA, he said.

At least 36 people were confirmed dead, but the search for bodies continued in what was shaping up to be Greece's worst train disaster. The toll was expected to rise.

At least 10 of the dead were train employees.

Rescue workers arry a body out of the wreckage. Photo: AFP

"This is the worst train accident in Greece," independent accident investigator Anastassios Dedes told Skai TV.

'Breaking windows and screaming'

Transport Minister Kostas Karamanlis held back tears as he vowed that the causes of the accident would be investigated. 

But train unionists have long claimed that insufficient funding was directed to safety systems in a network that is already one of the least efficient in Europe.

And over five years after Greek rail operator Trainose was sold to Ferrovie Dello Stato Italiane, safety systems are still not fully automated.

Many passengers said they had to make their own way out of the wreckage, in some cases smashing windows to break free.

"We couldn't see anything, but the train started jostling until it keeled over by 45 degrees," a young passenger told reporters at the scene.

"People were breaking windows and screaming, there was panic in the carriage," he said.

Greek Prime Minister Kyriakos Mitsotakis (R) visits the area of a crushed wagon after the train accident. Photo: AFP

Outside Larissa hospital, local mayor Kalogiannis said "streams" of ambulances were rushing in burn victims and amputees, while family relatives desperately searched for information on survivors.

"One man was crying for help, he had three children on the train," Kalogiannis said.

The passenger train, carrying over 350 people, had been travelling from the capital Athens to the northern city of Thessaloniki.

Most were students returning to Thessaloniki after a long holiday weekend.

The Larissa station master was arrested several hours after the accident and was charged with negligent homicide.

An emergency government meeting was organised after the crash and military hospitals in Thessaloniki and Athens have been put "on alert" in case they are needed.

A three-day period of mourning has been declared.