The Italian government declared a state of emergency in the quake-struck region of northeast Italy on Tuesday, where 5,000 people were camped out in temporary shelters amid fears of aftershocks.

The government declared a 60-day state of emergency for the area around Bologna, Modena and Ferrara and promised 50 million euros ($63 million) in aid to help rebuild houses and family-owned factories destroyed in the earthquake.

Owners of damaged property will also temporarily be exempt from property tax, the government said in a statement.

Prime Minister Mario Monti visited several of the quake-struck towns Tuesday and met the families of victims of Sunday's 6.0-magnitude quake, which killed six people and reduced homes and historic buildings to rubble.

Dozens of aftershocks have hit the region since the quake, with only two registering over 3.0-magnitude according to the Geophysics Institute.

Rescue workers in the so-called "red zone" in the town of Finale Emilia, the epicentre, said damaged buildings had remained stable since Monday, with no further significant collapses of weakened buildings.

"At the moment the percentage of houses declared uninhabitable is very low," said Demetrio Egidi, head of Italy's civil protection agency in Emilia-Romagna, where firemen were carrying out house-to-house controls to check for damage.

The region's priceless architectural treasures were worst hit, with churches, chapels and castles wrecked and famous frescoes destroyed.

"We don't yet know the extent of the damage to heritage, but as far as architectural structures go, it's been a real disaster," said Massimiliano Righini, a culture official for the town of Finale Emilia.

Thousands of people were camped out in parked cars in supermarket car parks or public squares amid fears that aftershocks might bring houses down, or in tent cities set up by the authorities.

"We hope that once people calm down, they will return to their homes," Egidi said, adding that the tent camps could hold up to 5,800 people.

Monti, who cut short a trip to the United States where he was attending a NATO summit, slept in the nearby city of Ferrara on Monday before heading to Sant'Agostino, where the clock was stuck at 4:05 am -- the hour the quake hit.

A relative of Nicola Cavicchi, 35, one of four factory workers killed, said: "It was a terrible quake, unthinkable that it should happen to us".

"It was fate. If he had been standing five metres away, nothing would have happened to him. He was just doing his job," the relative told reporters.

Sunday's quake rattled the cities of Ferrara -- a UNESCO World Heritage site -- as well as Bologna, Verona and Mantua and several smaller towns.

"Damage to businesses is going to run to no less than hundreds of millions of euros," a local branch of employers' organisation Confindustria said.

At least 200 businesses and 2,000 workers in the region would be severely affected, the organisation said. The left-wing CGIL union said the figure was likely to be much higher, with around 5,000 workers affected.

Monti's visit sparked a small demonstration by Sant'Agostino residents, who chanted anti-government slogans, complaining about tax hikes and austerity measures which they protest are strangling a country hit by recession.

"Thieves! Shame on you. You should have stayed home," they shouted, while another said Monti had just come to take advantage of the "media circus."

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.