In Pictures: Powerful earthquake strikes central and southern Italy
A powerful earthquake with a preliminary magnitude of 6.6 has rocked the same area of central and southern Italy hit by a quake in August and a pair of aftershocks last week.
It has sent already damaged buildings crumbling after a week of quakes that have left thousands homeless.
The head of Italy's civil protection agency, Fabrizio Curcio, said there were no immediate reports of deaths, but said some people had suffered injuries as numerous buildings that had resisted the previous shocks collapsed.
Residents already rattled by a constant trembling of the earth rushed into piazzas and streets after being roused from bed by the quake at 7.40am local time.
Many people had still been sleeping in cars or evacuated to shelters or hotels in other areas after a pair of strong jolts last Wednesday.
Television images showed nuns rushing out of their church and into the main piazza in Norcia as the clock tower appeared about to crumble. One had to be carried by firefighters, while another was supported as she walked.
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 August 24 earthquake that killed nearly 300 people, Arquata Mayor Aleandro Petrucci said: "There are no towns left."
"Everything came down," he said.
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.
Austria's governmental earthquake monitoring organisation said the quake was felt to varying degrees in the east and south of the country and all the way to the city of Salzburg. It says that at its strongest, residents in upper floors noticed a swaying sensation and a slow swinging of hanging objects.
The head of the civil protection authority in Italy's March region, Cesare Spuri, said there have been reports of buildings collapsing in many cities.
In Norcia, nuns knelt in prayer and a firefighter appealed to a priest to help maintain calm among dozens of residents gathered there, including some in wheelchairs.
The church, which had withstood the August earthquake in August and last week's aftershocks, was still standing but television pictures showed piles of stone had accumulated at the bottom of one wall. One stone was thrown metres into the centre of the piazza, illustrating the quake's force.
"We have to keep people calm. Prayer can help. I don't want people to go searching for family members," the firefighter appealed as cameras from SKY TG24 filmed.
The European-Mediterranean Seismological Centre put the magnitude at 6.6 or 6.5 with an epicentre of 132 kilometres north-east of Rome and 67 kilometres east of Perugia, near the epicentre of last week's quakes. The US Geological Survey put the magnitude at 6.6.
The German Research Centre for Geosciences put the magnitude at 6.5 and said it had a depth of 10 kilometres, a relatively shallow quake near the surface but in the norm for the quake-prone Apennine Mountain region.