Update 2: 'Four killed' in Italian earthquake

At least four people are reported to have been killed after an earthquake with a magnitude of 6.0 rattled parts of northern Italy.

Rescuers and witnesses said that buildings toppled and residents ran into the streets in the area around Bologna during the quake - one of the strongest ever to strike that part of the country.

The tremor took place at around 4 a.m. between Modena and Mantova, about 22 miles north-north-west of Bologna at a relatively shallow depth of 3.2 miles, the US Geological Survey (USGS) said.

Initial television footage indicated that older buildings had suffered damage: roofs collapsed, church towers showed cracks and the bricks of some stone walls tumbled into the street.

The damaged bell tower of a church in Santuario. Photo: Pierre Teyssot, AFP

News reports, citing emergency services, said three people were killed in Sant'Agostino di Ferrara when a ceramics factory collapsed. Another person was killed in Ponte Rodoni do Bondeno, the Ansa news agency reported.

Italy's Sky TG24 showed images of the collapsed ceramics factory where the two workers were reportedly killed. The structure, which appeared to be a hangar of sorts, had twisted metal supports jutting out at odd angles amid the collapsed roof.

Stefano Zeni, a worker in the factory, said: "This is immense damage, but the worst part is we lost two people."

TV reports also said two other people died of apparent heart attacks in the wake of the tremor.

"It was a strong one, and it lasted quite a long time," said Emilio Bianco, receptionist at Modena's Canalgrande hotel, housed in an ornate 18th century palazzo.

The hotel suffered no damage and Modena itself was spared, but guests spilled into the streets as soon as the quake hit, he said.

Many people were still awake at 4am in the town since it was a "white night", when shops and restaurants open all night. Museums were supposed to have remained open as well, but closed following the bombing of a school in southern Italy that killed one person.

The quake's epicentre was between the towns of Finale Emilia, San Felice sul Panaro and Sermide, but was felt as far away as Tuscany and northern Alto Adige.

The initial quake was followed about an hour later by a 5.1-magnitude aftershock, the USGS said, and was preceded by a 4.1-magnitude tremor.

In late January, a 5.4-magnitude quake shook northern Italy. Some office buildings in Milan were evacuated as a precaution and there were scattered reports of falling masonry and cracks in buildings.

In 2009, a devastating tremor killed more than 300 people in the central city of L'Aquila.