ATHENS: It took a bang, and just seconds to turn a long holiday weekend into a nightmare for hundreds of Greeks caught up in a deadly train collision on Tuesday night.

Tuesday's crash 220 miles north of Athens killed at least 36 people when a high-speed passenger train heading to the northern city of Thessaloniki careered into a freight train from the opposite direction, flying off the track and bursting into flames.

Witnesses said they felt a strong shudder, then a bang, then chaos.

First responders said people were flung out of the front carriages on impact, with victims found up to 40 metres away from the wreckage, and others trapped in blazing carriages.

Many of the victims were thought to be university students.

"Windows were being smashed and people were screaming," said a passenger on the fifth carriage. "One of the windows caved in from the impact of iron from the other train," the passenger told Skai TV as he took shelter under a nearby bridge, his face illuminated from the fire raging in the background.

There were about 350 people on the train, which passengers described as being two-thirds full with many young people.

"My child is not picking up the phone," one woman said as she waited at a train station in Thessaloniki. Another woman ran to embrace her daughter as she disembarked from a bus with survivors. "Mum don't, I'm hurt," the daughter replied.

Many passengers would have been returning home after a long holiday weekend marking the beginning of Greek Orthodox lent. Thessaloniki has a large student population.

"There was panic, cables (everywhere) fire, the fire was immediate, as we were turning over we were being burned, fire was right and left,” said 28-year old passenger Stergios Minenis.

Another passenger in one of the last carriages said he felt the train shake, then flip over.

"I managed to get out and went to the front, the train was bent at a 90 degree angle, half of it was hanging over the cliff burning. There were five people injured just where I stood," he said.

The Tempi valley, where the crash occurred, is a notorious spot for accidents. In 2003, 23 school children were killed in a bus crash there.

As morning broke, rescue crews trawled through a smouldering mangled mass of steel while cranes slowly removed pieces of the train.

They were still discovering victims hours later. ERT state TV showed one crew carrying what was thought to be a victim, covered in a white sheet, to an ambulance.