One worker was taken to hospital with serious injuries, and another was trapped under rubble following the partial collapse of a medieval tower near the Colosseum in central Rome.
Regional President Francesco Rocca said the worker in hospital was not in a life-threatening condition, while two more workers suffered minor injuries at the Torre dei Conti on Monday.
"We are trying to get him out alive, but the situation is complex because of the risk of further collapses," national fire department spokesman Luca Cari said about ongoing rescue efforts.
The 29-metre (95 ft) Torre dei Conti stands near one of the Eternal City's tourist hotspots, halfway along the Via dei Fori Imperiali, the broad avenue that leads from central Piazza Venezia to the Colosseum.
It suffered at least two collapses, according to videos posted online. On both occasions, clouds of dust came billowing out of the windows, along with the sound of collapsing masonry.
