ROME (AP) — The investigation into the violent head-on train crash in southern Italy that killed nearly two dozen people is focusing in particular on the antiquated telephone alert system used to advise station masters of trains running on the single track.

Recovery operations using a giant crane and rescue dogs continued through the night and into Wednesday to remove the mangled debris of the two commuter trains that slammed into one another just before noon Tuesday in the neat olive groves of Puglia.

After visiting the crash site, Premier Matteo Renzi declared it an "absurd" tragedy and vowed to investigate fully. His transport minister was to brief parliament later Wednesday.

Union leaders and railway police blamed human error, noting that the particular stretch of track between the towns of Andria and Corato didn't have an automatic alert system that would engage if two trains were close by and on the same track. Rather, news reports said, the system relied on station masters phoning one another to advise of a departing train.

"Surely one of the two trains shouldn't have been there," said railway police Cmdr. Giancarlo Conticchio. "And surely there was an error. We need to determine the cause of the error," Conticchio said.

Italian Red Cross workers on Wednesday were shuttling family members to the morgue in Bari, the regional capial, to help identify the dead. Coroner Franco Introna told the ANSA news agency that 22 bodies were at the morgue, with a 23rd expected to arrive later from Andria.

Passengers described being thrown forward violently at the moment of impact, and then trying to free themselves from the tangle of metal, body parts and debris in the scorching midday sun.

"I don't know what happened, it all happened so quickly, I don't know," one woman, eight months pregnant, told The Associated Press. "I saw my mother on the ground, my father and my sister bleeding, I don't know, I don't know, even I don't know."

One elderly couple described their ordeal to local television Telesveva. The man, his head covered in gauze, said he was knocked to the ground, while his wife, still barefoot, described how she came across body parts as she freed him.

"I pulled him from under the debris, myself barefoot, from under the debris and metal," the woman, who was not identified, told local TV. "I went to my husband screaming. I pulled him by the legs and feet. I climbed past people in pieces, how sad. There was nothing I could do."

Corato Mayor Massimo Mazzilli said debris was scattered over the countryside.

"It's a disaster as if an airplane fell," Mazzilli said on his Facebook page, where he posted photos of the crash.

Pope Francis sent a telegram to the archbishop of Bari, Monsignor Fracnesco Cacucci, saying he shared in the pain of so many families. He said he was mourning those who died and praying for the injured to recover quickly.

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."