There was also construction being done on the first floor of the four-story Torre Annunziata apartment building, near Naples and Pompeii, which reportedly housed two families.
It is feared families are trapped underneath the rubble, although no casualties have yet been reported.
Some 30 firefighters were deployed to the scene, using long retractable ladders to assess the stability of those parts of the building still standing.
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.
Italy's fire service shared a brief video of its earliest rescue efforts via Twitter, saying that at the time of filming, nobody had been found in the rubble.
The renovation work, or vibrations from the railway, are suspected causes of the collapse, the BBC said.
Witnesses reported there was no explosion before the building collapsed, but that a freight train had passed on nearby rail tracks.
Torre Annunziata Mayor Vincenzo Ascione said seven people are missing.