Rescue crews operate at the site of a crash, where two trains collided, near the city of Larissa, Greece, March 1, 2023. Photo: REUTERS/Alexandros Avramidis

Dozens more were injured in the crash and the fire that followed. Officials said the death toll was expected to rise further.

A station master was arrested as investigators tried to understand why the two trains had been on the same track.

"There was panic ... the fire was immediate, as we were turning over we were being burned, fire was right and left," said Stergios Minenis, a 28-year-old passenger who jumped to safety from the wreckage.

A passenger who escaped from the fifth carriage told Skai TV: "Windows were being smashed and people were screaming ... One of the windows caved in from the impact of iron from the other train."

Rescuers continued to scour through the smouldering mangled mass of steel in the morning, and cranes lifted derailed passenger carriages, their windows blown out. One carriage stood on its side at almost 90 degrees from the rest of the wrecked train, with others tilting precariously.

Flags flew at half-mast in Athens in a tribute to the victims of the crash, as the government declared three days of national mourning.

Many of the victims were thought to be university students on their way back from a long holiday weekend.

"It's an unthinkable tragedy. Our thoughts today are with the relatives of the victims," Greek Prime Minister Kyriakos Mitsotakis said at the site of the crash, looking shattered.

The local station master, in charge of signalling, has been arrested and charged with causing mass deaths through negligence and causing grievous bodily harm through negligence, a police official said.

The 59-year-old man has denied any responsibility for the accident, attributing it to a possible technical failure, the official said.

The crash occurred as the passenger train that was headed to the northern Greece city of Thessaloniki from the capital Athens emerged from a tunnel near the town of Larissa.

Government spokesman Giannis Oikonomou said the two trains had been running towards each other on the same track "for many kilometres" before the crash.

Yiannis Ditsas, head of the Greek railway workers union told Skai television that automatic signalling at the spot of the crash had not been working. There was no immediate official comment on this.

The passenger train was carrying 342 travellers and 10 crew, while two crew were on the cargo train, according to Hellenic Train data.

Sixty-six of those injured were hospitalised, six of whom in intensive care, a fire brigade official said.