A canine unit and cranes have been deployed to aid search and rescue efforts following the deadly crash.

Rescuers in Spain are searching for victims and survivors a day after a train struck another from behind, killing 68 people, in the country’s second high-speed rail disaster this year.

Emergency workers and rescue teams with sniffer dogs continued to look for victims on Thursday morning, a day after the collision in Toledo province, central Spain.

Cranes were in place to help shift the carriages as police and soldiers helped to pick through the wreckage strewn down the gravel slope where at least three train carriages were derailed by the impact.

Esther Padilla, a spokeswoman for the regional government of Castilla-La Mancha, told TVE that teams were working “very carefully, because we still cannot say with certainty that there are no more victims trapped in the twisted wreckage”.

“A canine unit was deployed yesterday. They will go back in today to make sure that nobody else remains there,” she added.

She said 53 people remained in hospital, with 15 in critical care.

Three days of mourning have been declared for those killed in the accident.

Wednesday’s crash followed a similar fatal accident earlier this year involving the same rail companies on the same line.

In January, 46 people died when a train jumped the track and slammed into the side of another going in the opposite way in southern Spain.

The collision has reopened a national debate about the safety of Spain’s high-speed rail network, the biggest in Europe and, until recently, a source of national pride.

Transport Minister Oscar Puente said the crash happened after several trains stopped automatically due to a signal failure.

A state-run Renfe train was then authorised to proceed at normal speed even though a stationary Iryo-operated train was ahead.

Prime Minister Pedro Sanchez visited the crash site on Wednesday. He pledged an investigation into the latest collision and promised improvements to prevent another tragedy like the two that have shaken trust in a rail system that carried 45 million travellers last year, including millions of tourists.

“It is clear that we need to reinforce the safety of our train service to rebuild the trust in our high-speed rail,” Sanchez said. “It is not acceptable for a country like Spain to endure two high-speed train accidents in the same year.”

The Spanish train drivers’ union, SEMAF, said that it does not want to speculate on the cause of the crash.

“We wish to exercise caution until we have a detailed understanding of exactly what happened, so as not to engage in speculation,” SEMAF said in a statement late on Wednesday.

Meanwhile, SEMAF said train drivers have gone ahead with a previously planned strike to push for more railway safety and structural change.