A powerful earthquake has rocked the same area of central and southern Italy hit by quake in August and a pair of aftershocks in recent days, sending already quake-damaged buildings crumbling and affecting thousands without homes.
The 6.6 magnitude quake is thought to be the strongest to hit the country in three decades.
Residents already rattled by a constant trembling of the earth rushed into piazzas and streets after being roused from bed by Sunday's 7:40am quake.
Many people still had been sleeping in cars or evacuated to shelters or hotels in other areas after a pair of strong jolts last Wednesday.
There were no immediate reports of injuries or deaths.
Television images showed nuns rushing out of their church and into the main piazza in Norcia as the clock tower appeared about to crumble.
The mayor of quake-hit Ussita said a huge cloud of smoke erupted from the crumbled buildings.
"It's a disaster, a disaster!" Mayor Marco Rinaldi told the ANSA news agency. "I was sleeping in the car and I saw hell."
Another hard-hit city, Castelsantangelo sul Nera, also suffered new damage.
In Arquata del Tronto, which had been devastated by the 24 August earthquake that killed nearly 300 people, Arquata Mayor Aleandro Petrucci said: "There are no towns left. Everything came down."
The 6.6 magnitude quake is believed to be the strongest to hit the country since 1980.
A 6.9-magnitude quake in southern Campania that year killed some 3,000 people and caused extensive damage.
The quake was felt throughout the Italian peninsula, with reports as far north as Bolzano and as far south as Bari. Residents rushed into the streets in Rome, where ancient palazzi shook, swayed and lurched for a prolonged spell.
The German Research Centre for Geosciences put the magnitude at 6.5 and said it had a depth of 10 kilometers, a relatively shallow quake near the surface but in the norm for the quake-prone Apennine Mountain region.
Additional reporting by agencies
