At least 68 people have died and dozens have been injured after a high-speed train struck a stationary train in central Spain, prompting questions over railway safety after a second major disaster this year.

The collision happened just after 09:00 local time (08:00 GMT) on Wednesday between Mora and Orgaz, about 140km south of Madrid. Several carriages fell down an embankment and one caught fire.

An Iryo train carrying 147 passengers had stopped because of a computer failure, Transport Minister Óscar Puente said. The operator said it was struck from behind by a Renfe train carrying 397 passengers. The moving train was travelling from Madrid to Seville.

Puente attributed the crash to a computer failure followed by human error. He said a round-the-clock control centre in Madrid, which takes over during system failures, had made an “inexplicable” decision to instruct the trains to move again without speed restrictions.

That account has drawn a challenge from the CSIF trade union, which demanded Puente’s resignation. It accused him of “scapegoating” a traffic manager rather than taking responsibility. The minister’s explanation does not settle whether negligence occurred: Prime Minister Pedro Sánchez has promised to establish that.

Survivors described passengers thrown through carriages, trapped among seats and breaking windows to escape. Salvador Arriza, 62, who was on the Renfe train, called the impact “brutal”. Tangui Binier, 22, aboard the Iryo service, described smoke, flying suitcases and an overturned train. His father carried a girl with a broken hip from the wreckage.

Journalist Antonio Jiménez Barca suffered a head injury; Sebastián Herrero, 46, said he was airborne for four or five seconds. Another survivor described a woman dying in his arms. Photographs show a length of railway track piercing a carriage.

Dozens of ambulances attended, with a helicopter evacuating the most seriously injured. The Civil Guard said DNA samples from relatives would be needed to identify some victims.

“The whole of Spain is grieving”, Sánchez said at the scene. Most parties cancelled Wednesday’s campaign events. Vox leader Santiago Abascal refused, saying mourning should not be used to silence criticism of rail infrastructure.

Opposition People’s Party leader Alberto Núñez Feijóo said Spain had a right to know what was happening to its infrastructure and that any safety-system failures must be addressed firmly.

A January crash near Córdoba, further south on the same line, killed 46 people. Sánchez called two serious crashes in one year unacceptable. Wednesday’s disaster is among Europe’s worst in modern history and Spain’s deadliest for 13 years, since 80 people died near Santiago de Compostela in 2013.