Two regional trains packed with students and commuters collided head-on in southern Italy on Tuesday, killing at least 23 people, ANSA news agency reported, quoting local officials and politicians.
The number of injured had risen to more than 50 several hours after the accident, reported ANSA, citing Health Ministry officials.
It was one of the nation's worst-ever train accidents.
First responders at the site described horrific scenes.
"I've seen horrible, awful things," one police officer told ANSA. "I saw dead people. People who were calling for help. People who were crying. They were the worst things I've seen in my life."
Massimo Mazzili, mayor of the nearby town of Corato, took to Facebook to try to describe the scene.
"It's a catastrophe. It looks like a plane crashed."
Giuseppe Corrado, vice president of Bari-Andria-Barletta, appealed for blood donors to come forward as emergency services treated dozens of injured.
Corrado said four people were in a critical condition.
Among the injured was a toddler who was pulled from the wreckage, ANSA reported. The agency later said that at least one of the drivers was dead.
According to local media reports, the regional trains were packed with students and commuters at the time of the accident, around 11:30 am (0930 GMT).
The two trains crashed on a single track between Corato and Andria, north of the port city of Bari.
Broadcast footage showed the front carriages of both trains completely destroyed by the collision.
Italian media reported that many passengers were still trapped in the wreckage at the crash site, which is proving difficult for rescuers to access.
The trains, both operated by private railway company Ferrotramviaria, are thought to have been carrying four carriages each.
Italian Prime Minister Matteo Renzi has called for a prompt investigation into the cause of the crash and expressed his condolences to the families of the victims.
But getting answers may take time.
"We still don't know what the cause of the crash was," said Transportation Minister Graziano Delrio, adding that an investigation would be necessary.
Legambiente, a major Italian environmental organization, said the problem might be because of the fact that the old tracks in that region of the country had no automatic braking systems and that little money had been invested in the system.
Human error could not be ruled out. There were no reports of bad weather at the time.