A powerful earthquake has rocked the same area of central and southern Italy hit by quake in August and two 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 pictures: Most powerful earthquake for three years hits Italy Show all 13 1 /13 In pictures: Most powerful earthquake for three years hits Italy In pictures: Most powerful earthquake for three years hits Italy Fractures on a road in Norcia after the strong earthquake in central Italy EPA/Matteo Crocchioni In pictures: Most powerful earthquake for three years hits Italy The bell tower of St. Augustine's church destroyed after the strong earthquake in central Italy, Amatrice EPA/Massimo Percossi In pictures: Most powerful earthquake for three years hits Italy Nuns rest on a bench after been evacuated from their monastery following an earthquake in Norcia, Italy REUTERS/Remo Casilli In pictures: Most powerful earthquake for three years hits Italy The church of the Madonna of the Angels is seen partially collapsed following an earthquake along the road to Norcia, Italy Reuters In pictures: Most powerful earthquake for three years hits Italy A powerful earthquake rocked the same area of central and southern Italy in August and a pair of aftershocks last week, sending already quake-damaged buildings crumbling after a week of tremors that have left thousands homeless Vigili Del Fuoco/Italian Firefighters via AP In pictures: Most powerful earthquake for three years hits Italy A 6.6 magnitude earthquake struck 6km north of Norcia, Italy, EPA In pictures: Most powerful earthquake for three years hits Italy A 6.6 magnitude earthquake struck 6km north of Norcia, Italy EPA/Alberto Orsini In pictures: Most powerful earthquake for three years hits Italy People are evacuated from an hospital following an earthquake in Rieti, Italy REUTERS/Emiliano Grillotti In pictures: Most powerful earthquake for three years hits Italy L'Aquila Mayor Massimo Cialente speaks on his mobile telephone as he checks the damage after the strong earthquake in L'Aquila, central Italy EPA/Alberto Orsini In pictures: Most powerful earthquake for three years hits Italy Italian firefighters escort a frightened woman out of a building just as an aftershock rattled Norcia, central Italy AP Photo/Gregorio Borgia In pictures: Most powerful earthquake for three years hits Italy A view of Amatrice village completely destroyed after the strong earthquake in central Italy EPA/Massimo Percossi In pictures: Most powerful earthquake for three years hits Italy A firefighter and an alpine soldier look at rubble in the hilltop town of Amatrice as an earthquake with a preliminary magnitude of 6.6 struck central Italy Massimo Percossi/ANSA via AP In pictures: Most powerful earthquake for three years hits Italy A handout map released by the US Geological Survey (USGS) shows the location of the earthquake striking around 68km east-southeast of Perugia, Italy EPA

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.