An underground water mains break along Florence's picturesque Arno River has created a 200-metre-long sinkhole.
Firefighters asked residents of nearby palazzi to evacuate voluntarily as there was no water or lighting in the area.
The sinkhole has buried at least 20 parked cars.
Hours after the pre-dawn break, authorities were trying to determine on Wednesday whether the weakened asphalt could withstand the weight of a crane to extract the waterlogged cars that fell into the hole.
Mayor Dario Nardella stressed that the underground flooding was the result of a gash in a diameter pipe - one of the major water conduits in the neighbourhood - and not a leak in the banks of the Arno.
The scene is near the famed Ponte Vecchio bridge, a favourite spot for tourists shopping for jewellery.