Several thousand Italians spent the night in cars or temporary shelters after a strong earthquake hit the northeast Sunday, killing six people and reducing homes and historic buildings to rubble.

Emergency services said dozens had also been injured in the magnitude 6.0 quake, which struck the densely-populated industrial Emilia Romagna region in the middle of the night, sending panicked residents running into the streets.

Fearful of staying in weakened buildings, hundreds of people spent the night in their cars while others took shelter in temporary accommodation where local authorities provided beds, tables and chairs.

Prime Minister Mario Monti left early from the United States, where he was attending a NATO summit, following the quake which struck at 0200 GMT Sunday and a deadly school attack on Saturday.

The disaster hit just over three years after a 6.3 magnitude quake devastated the central city of l'Aquila in March 2009, killing some 300 people and leaving tens of thousands homeless.

During the night at least 24 aftershocks were felt in the area, at least four of them with a magnitude of at least 3, while heavy rain fell.

Four of the dead were night-shift workers in factories which collapsed, including two people who were crushed when the roof of a ceramics factory caved in the town of Sant'Agostino.

A 37-year-old German woman and another woman aged over 100 reportedly died from shock, while 3,000 people have been evacuated from their homes and hospitals were also cleared as a precautionary measure.

"I went out because I felt the house moving. Furniture was falling over. It was chaos. Everyone was running in every direction," said retired electrician Claudio Bignami, 68.

Aldra Bregoli, 73, who had pulled on a sweater over her nightgown, said: "I had to get out quickly. I can't go back home. I'm afraid."

Italian television showed many historic buildings, including churches, reduced to rubble. Cars were crushed under falling masonry, and the Civil Protection Agency evacuated hundreds of elderly and vulnerable people to makeshift communal shelters in Finale Emilia and towns near the epicentre.

"According to first reports, damage to the cultural heritage is significant," the culture ministry said after the quake rattled the cities of Bologna, Ferrara, Verona and Mantua.

Authorities said the quake's epicentre was the commune of Finale Emilia, 36 kilometres (22 miles) north of Bologna, at a depth of only 5.1 kilometres.

The region is Italy's industrial heartland but also home to priceless architectural and art treasures. The historic centre of Ferrara is classified as a UNESCO World Heritage site.

The roof of a recently renovated sixth-century chapel in San Carlo, near Ferrara, caved in, exposing statues of angels to the elements.

Claudio Fabbri, a 37-year-old architect, told AFP the restoration had taken eight years. "Now there's nothing left to do," he said despondently.

Warehouses storing more than 300,000 wheels of Parmesan and Grana Padano, a similar cheese, with an estimated value of more than 250 million euros ($320 million), also collapsed, an industry official said.

One of the men killed in the ceramics factory collapse, Nicola Cavicchi, 35, "wanted to go to the seaside but because of the bad weather forecast he decided to go to work to replace a colleague who was sick," a family member told local media.

A 29-year-old Moroccan man was killed by a falling girder when a factory building collapsed in the small town of Ponte Rodoni di Bondeno.

The body of a fourth night-shift worker was found under fallen masonry at a factory in a nearby village.

In Finale Emilia, firefighters rescued a five-year-old girl who was trapped in the rubble of her house after a rapid series of phone calls between a local woman, a family friend who was in New York and emergency services.

A 5.1 magnitude aftershock struck Sunday afternoon, triggering the collapse of several structures already weakened, with a firefighter left seriously injured after falling from a wall.

Yet in a show of calm nerves, officials opened polls as planned for the second round of local elections in the cities of Piacenza, Parma, Budrio and Comacchio.

European Commission chief Jose Manuel Barroso said Brussels was "ready to provide swiftly any assistance that may be requested."