People were pulled from the rubble in towns across central Italy and 20 were injured after buildings collapsed when Sunday`s earthquake hit "like a bomb".
It struck at the heart of a region already struggling to rebuild after being devastated by a series of quakes, including one in August that left 298 people dead and two massive tremors four days ago.
More than 3,000 people have been forced to flee their homes following Sunday`s quake, according to the national civil protection agency.
However, no one is reported to have been killed or seriously injured, possibly because many people had already left their homes after last week`s tremors.
The series of quakes have now forced a total of almost 8,000 people to seek refuge in hotels and shelters, with many more sleeping in tents, cars or campers.
Sunday`s quake struck three miles north of the town of Norcia - near Perugia in the Umbria region.
The magnitude was recorded by the US Geological Service at 6.6, with a depth of six miles (10km).
Seismologist Gianluca Valensise, of Italy`s National Institute for Geophysics and Vulcanology, said it had a "geodynamic link" to the one in August.
In Norcia, nuns and monks fled into the street as a cathedral and a church, which had been left standing after the recent earthquakes, crumbled during morning worship.
The monks of Norcia said the 14th century Basilica of St Benedict had been "flattened" and some knelt in the rubble of the landmark.
<St Mary Argentea church, known for its 15th century frescoes, and the town`s ancient walls were also seriously damaged. The town hall clock tower appears perilously close to collapse.
Norcia city assessor Giuseppina Perla said: "It`s as if the whole city fell down."
The town`s deputy mayor, Pierluigi Altavilla, said: "It was like a bomb went off. We are starting to despair. There are too many quakes now, we can`t bear it anymore."
Italian Prime Minister Matteo Renzi pledged to rebuild all of the homes and churches destroyed by the latest earthquake and said Italy`s "soul is disturbed".
Priests have been told not to hold masses in churches in the region because of the risk.
In Cascia, 13 miles south of Norcia, a hospital had to be evacuated and children in some towns were told schools would not open on Monday. There were reports of 15,000 homes without power.
Aleandro Petrucci, the mayor of Arquata del Tronto, another town battered by the series of quakes, declared: "There are no towns left. Everything`s come down."
In Rome, more than 100 miles away, cracks appeared in buildings and the underground train network was shut for structural checks.
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