Two Italian commuter trains collided head-on Tuesday in the southern region of Puglia, killing at least 20 people and injuring scores more, officials said. At least two passengers were pulled alive from the crumpled wreckage as the rescue operation ground on in the scorching heat. Giuseppe Corrado, vice president of the province of Andria, told reporters at the scene that the death toll stood at 20 and that the local hospital needed blood. Another official stressed the final toll would not be known until the train cars had been pulled apart; a giant crane arrived at the scene to remove the mangled debris. The two trains, each with four cars, collided head-on in an olive grove on flat terrain between the towns of Andria and Corato on a line with just a single track. The accident occurred around 11:30 a.m. some 50 kilometers (30 miles) northwest of the Puglia regional capital, Bari. "It's a disaster as if an airplane fell," Corato Mayor Massimo Mazzilli said on his Facebook page, where he posted photos of the crash. Italian Premier Matteo Renzi pledged a thorough investigation and returned to Rome from Milan to monitor the situation. His transport minister, Graziano Delrio, as well as local prosecutors were at the scene. "We must begin to understand the causes of this tragedy that has saddened the whole country," Delrio said at the site, announcing a commission of inquiry. "The crash was certainly violent. Extremely violent." The cars clearly slammed into one another: They rested crumpled together like an accordion, off the tracks at sharp angles. News reports said rescue workers pulled a small child alive from the rubble. Riccardo Zingaro, the chief of the local police in Andria, told Sky it was "a great tragedy." Some rescue workers seemed overwhelmed by the scene and the heat. "The impact was significant, and we are now verifying the consequences," said Giovanni De Siervo of Italy's civil protection service. A field hospital was set up in the nearby fields to treat the numerous injured, who were also being transported to hospitals. "Some of the cars are completely crumpled and the rescuers are extracting people from the metal, many of them injured," Zingaro told ANSA at the scene. Italy's premier, Renzi, said the train crash "is a moment of tears" and pledged not to stop investigating until a cause was determined. The trains were operated by a private, Bari-based rail company, Ferrotramviaria, that connects the city of Bari with Puglia towns to the north and the airport. Ferrotramviaria's website said its fleet comprises 21 electric trains, most with four cars each. The line serves mostly students and commuters. In a phone interview with state TV, Ferrotramviaria director general Massimo Nitti said the dynamics of what went wrong are still to be determined, but it is clear "one of the trains wasn't supposed to be there" at the same time as the other.