Rescuers searched late into the night Wednesday for survivors amid the mangled, burned-out wrecks of two trains that collided in northern Greece, killing at least 43 people and crumpling carriages into twisted steel knots in the country’s deadliest rail crash.

The impact just before midnight Tuesday threw some passengers into ceilings and out the windows.

Greek Prime Minister Kyriakos Mitsotakis called the collision of the passenger train and a freight train “a horrific rail accident without precedent in our country,” and pledged a full, independent investigation.

He said it appeared the crash was “mainly due to a tragic human error,” but did not elaborate.

The train from Athens to Thessaloniki was carrying 350 passengers, many of them students returning from raucous Carnival celebrations. While the track is double, both trains were traveling in opposite directions on the same line near the Vale of Tempe, a river valley about 380 kilometers (235 miles) north of Athens.