Firefighters and other emergency services are continuing to hunt through the wreckage of the trains, which were travelling along a single track between the towns of Corato and Andria when they collided at about 11.30am.
The total number of people travelling on each of the four-carriage trains is not yet known, although 50 people are estimated to have been injured. The severity of some of the injuries means that the death toll is likely to rise.
The vice-minister of transport, Riccardo Nencini, told RAI the lack of an automated security system was probably one of the causes of the crash.
Nicola Giorgino, the mayor of Andria, said the crash was particularly tragic since work was to begin within a few months to build a second track on the route.
The Trani prosecutor, Francesco Giannella, said the delay in the track-doubling work would be part of the investigation. “We will investigate the delays of the work on the line and the deficiencies in the security system,” the Ansa news agency quoted Giannella as saying.
Last month, the private rail company operating the line, Ferrotramviaria, announced a call for tenders to add a second track. Since the accident there has been criticism that the slow pace of public works in Italy meant the works were not carried out more promptly.
Ferrotramviaria issued a brief statement after the crash in which it offered condolences to the families of victims and said the company felt their pain. One of the train drivers is believed to be among the victims, while the other is reported as being in a serious condition in hospital.
Italy has hailed the rescue of a six-year-old boy, Samuele, who was shown cartoons on a smartphone by a fireman while colleagues cut him free from the wreckage. The boy asked about his grandparents, who remain unaccounted for, Italian media reported.
Pope Francis on Wednesday sent a blessing to those affected by the crash.
More about:






