The wreckage of a crumpled wagon after it collided with another train in Italy. Picture: AP

Two passengers were pulled alive from the crumpled wreckage as the rescue operation took place in the scorching heat.

Giuseppe Corrado, Vice-President of the province of Andria, said the death toll stood at 20 and that rescue operations were continuing. Another official stressed the final toll would not be known until the wreckage had been pulled apart.

The two trains, each with four cars, collided head-on at noon local time in an olive grove on flat terrain between the towns of Andria and Corato, 50km northeast of the Puglia regional capital, Bari.

Italian Premier Matteo Renzi pledged a thorough investigation and returned to Rome from Milan to monitor the situation.

Riccardo Zingaro, chief of police in Andria, said it was “a great tragedy”.

Some rescue workers seemed overwhelmed by the scene and the heat.

A photograph of the crash showed cars crumpled together like an accordion and forced off the tracks at sharp angles.

A field hospital was set up in the nearby fields to treat the scores of injured, who were also being transported to hospitals. “Some of the cars are completely crumpled and the rescuers are extracting people from the metal,’’ Mr Zingaro said.

AP