ROME (AP) — A speeding out-of-service train slammed into a group of workers doing nighttime track maintenance in northern Italy on Thursday, killing five of them, authorities said.

The crash occurred shortly after midnight at a station in Brandizzo, a town in Italy’s Piedmont region. Piedmont Gov. Alberto Cirio provided the death toll and said the accident’s cause was under investigation.

Brandizzo Mayor Paolo Bodoni said there were indications that the crew of the train was unaware there were workers on the tracks, reported La Stampa, a newspaper in Piedmont’s main city, Turin.

State radio initially said authorities had estimated that the train was moving at about 160 kilometers per hour (100 mph). But a preliminary investigation by railway police later lowered the speed estimate to about 100 kilometers per hour (about 62 mph), the Corriere della Sera newspaper said.

The train consisted of an engine car and 11 empty passenger cars that it was transporting, Corriere della Sera said.

“For sure there was a human error,” Transportation and Infrastructure Minister Matteo Salvini said.

“The first information reaching me refers to a scarcity of communication between the (work) team and who should have signaled the passage of the train, but we need to see what really happened,” Bodoni was quoted as saying.

Two workers who avoided being hit were being treated for shock at a hospital, La Stampa said.

Various unions representing train maintenance workers vowed to stage a strike to protest the crash and to commemorate the victims, Italian media said.

Pope Francis was asked about the crash by Italian reporters during his flight late Thursday to Mongolia. He called workplace deaths a “calamity and an injustice.” Such deaths, he said, “always occur because of a lack of care. Workers are sacred.”