Rescuers work amid the rubble of a building that collapsed, left, in Torre Annunziata, near Naples, southern Italy, Friday, July 7, 2017. A five-story apartment block collapsed early Friday near the southern Italian city of Naples, and authorities were digging by hand to find anyone who may have been trapped. (Ciro Fusco/ANSA via AP)

Rescuers work amid the rubble of a building that collapsed, left, in Torre Annunziata, near Naples, southern Italy, Friday, July 7, 2017. A five-story apartment block collapsed early Friday near the southern Italian city of Naples, and authorities were digging by hand to find anyone who may have been trapped. (Ciro Fusco/ANSA via AP)

MILAN (AP) — Rescue workers found the bodies of three people in the rubble of a five-story apartment building that partially collapsed south of Naples early Friday, firefighters said.

Crews were digging mostly by hand to search for seven people reported missing in the residential building in the seaside town of Torre Annunziata, four kilometers (three miles) from the Pompeii archaeological site.

The cause of the collapse remained unknown, but authorities were investigating whether it was related to renovation work in the building that stood near a passenger rail line.

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Officials had said seven people, including two children, from two families were missing. An elderly resident who had been believed to be inside was later accounted for.

Witnesses said they did not hear an explosion before the collapse sometime after 6 a.m., but that a train had just passed by the building, according to the ANSA news agency.

Images show the structure partially collapsed, revealing the interiors of some apartments. Some 80 rescue workers were passing hand-dug rubble out in buckets, as firefighters on long, retractable ladders checked the stability of the section that remained intact.

Firefighters asked for silence among onlookers during the search in hope of hearing survivors, and the work was paused periodically to allow sniffer dogs to check the scene.

The train line that passes Mount Vesuvius and connects Naples with such tourist sites as Pompeii and the Amalfi coast was temporarily closed after the collapse.

The Italian railway said in a statement that the vibrations from passing trains have no impact on the stability of adjacent buildings.