A five-storey apartment building has partially collapsed along a railway line near the southern Italian city of Naples, and authorities are digging by hand to find anyone trapped.

Firefighters said up to eight people may be buried in the rubble in the seaside town of Torre Annunziata, three miles from the Pompeii archaeological site.

Mayor Vincenzo Ascione was quoted by the Ansa news agency as saying two families were missing, including two children.

Witnesses said there was no explosion before the collapse, but a train had just passed by on adjacent tracks, according to Ansa .

Images show the structure partially collapsed, revealing the interior of some apartments.

About 30 rescue workers were removing rubble by hand, passing it out in buckets, as firefighters on retractable ladders checked the stability of the section that remained intact.

At one point, the digging was paused while a sniffer dog checked the scene.

News reports indicated that reconstruction work was being carried out on the building before the collapse. The mayor said it was not immediately clear if there was a connection between the work and the collapse.

The train line that passes Mount Vesuvius and connects Naples with such tourist sites as Pompeii and the Amalfi coast has been closed.

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