Two trains collided head-on near the city of Larissa in central Greece late Tuesday, killing at least 36 people and injuring dozens more.
The trains — a passenger train and a cargo train — collided near the entrance of a tunnel.
A station master in charge of signaling has been arrested, reported AFP, as investigators work to identify why the trains were traveling on the same track.
Greek Prime Minister Kyriakos Mitsotakis said that human error was to blame for the collision of the country’s worst rail tragedy.
“Everything shows that the drama was, sadly, mainly due to a tragic human error,” Mitsotakis said in a televised speech on Wednesday. He is seeking re-election this year.
Journalist Marina Rigou told the BBC that the trains were traveling at high speeds because the operators were not aware the other was coming. She added that the collision was so severe the front two carriages of one train “just disappeared.”
The passenger train was traveling to Athens from Thessaloniki, and many of the some 350 on board are thought to be young people heading back to their studies after a three-day festival celebrating the Greek Orthodox lent holiday.
“It is very difficult what we are experiencing today as a country. We are talking about an unspeakable tragedy,” Greek Prime Minister Kyriakos Mitsotakis said in a statement after visiting the site.
“Our thoughts today are first and foremost with the victims’ relatives. Our duty is to treat the wounded and from there to identify the bodies. From there, one thing I can guarantee: we will find out the causes of this tragedy and do everything in our power to make sure it never happens again,” he said.