Thousands of people prepared to spend a second night sheltering in cars and tent cities in northeast Italy Monday after a strong earthquake killed six people and caused massive damage.

Sunday's 6.0-magnitude quake reduced homes and historic buildings to rubble in sparsely populated countryside around the city of Ferrara, Italy's industrial heartland but also home to priceless architectural treasures.

Firefighters and police made house-to-house checks and rescuers set up four tent cities in Finale Emilia -- the epicentre of the quake -- to provide shelter for thousands of people, with many still too traumatised to return home.

In all some 5,000 people have been put up in various shelters in Modena and Ferrara, said the latter's prefect, Luigi Mauriello.

Hospital evacuees were also being cared for in temporary structures.

"We're worried we might be here a long time. Our house is more than 100 years old," said Maria, a pensioner, as she stood under an umbrella in the rain outside a large blue tent set up by Italy's civil protection agency.

Dozens of aftershocks were felt through the night and heavy rains lashed the area, hampering the efforts of emergency workers who arrived from all over Italy and were operating around the clock to offer food and shelter.

Gas, water and electricity supplies had been cut in many areas and rubble and roof tiles still lay strewn in the streets of dozens of villages.

"We'll stay here until the situation calms down," Sebastiano Lucchi, the manager of one of the tent camps in Finale Emilia, told AFP.

Prime Minister Mario Monti, who cut short a trip to the United States where he was attending a NATO summit, was due to visit the hardest-hit areas on Tuesday.

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

Six people were killed in Sunday's quake, including four night-shift workers in collapsed factories. A 37-year-old German woman and another woman aged over 100 reportedly died from shock while about 50 other people were injured.

The quake rattled the cities of Ferrara -- a UNESCO World Heritage site -- as well as Bologna, Verona and Mantua and several smaller towns in what one Italian newspaper dubbed "Nightmare Night".

Many historic buildings, including churches and castles, were reduced to rubble while cars were crushed under falling masonry, and in Finale Emilia the town's clock tower was dramatically sliced in two.

In Sant'Agostino the clock was stuck at 4:05 am -- the hour the shock hit.

The roof also caved in at a recently renovated 16th-century chapel in San Carlo, exposing statues of angels and a crucifix to the elements. Fragments of the church's famous frescoes could be seen in the rubble.

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.

Giancarlo Rivelli, one of a team of engineers helping to inspect buildings, said: "There's damage to the psychological heritage here.

"People identify with these buildings. They're part of their life."

Rivelli explained that one of the problems was that some of the old buildings had been sloppily renovated, for example with reinforced concrete.

"It's like trying to cure a hunchback by putting a 100-kilogramme (268-pound) weight on his shoulders," he said.

Warehouses storing more than 300,000 wheels of Parmesan and Grana Padano, a similar cheese collapsed.

The Emilia Romagna region has some of Italy's richest farmland and is known for many delicacies including Parmesan, Parma ham, balsamic vinegar from Modena and Bolognese sauce, which are exported around the world.

In all, some 250 million euros (�320 million) of farm products are estimated to have been lost as a result of the quake, an industry official said.

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

Yet in a show of calm, officials opened polls as planned for the second round of local elections in several cities and voting continued on Monday.

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