The powerful quake hit shortly after 4am local time, felling homes and causing damage to several historic buildings in the area. Thousands of people fled into the streets.
According to Italian media reports, four of the fatalities were workers on night shifts.
Three people were reported to have been killed when the steel roof of a ceramics factory collapsed in the town of Sant'Agostino di Ferrara.
Another person was killed at a polyester factory in Ponte Rodoni do Bondeno.
The mother of one of the victims told state television: "He wasn't supposed to be there. He changed shifts with a friend who wanted to go to the beach."
Two women - one believed to be over 100-years-old and another aged 37 - were reported to have died after suffering heart attacks brought on by panic during the quake.
A five-year-old girl trapped in rubble after her home collapsed was rescued by firefighters in Finale Emilia after frantic phone calls between a local resident, a family friend in New York and emergency services, it was reported.
There are fears the death toll could rise still with reports of people missing.
Ancient bell towers in towns were damaged, several church steeples also partly collapsed, while hospitals were evacuated as a precautionary measure.
The roof of the cathedral in Mirandola collapsed. "Our schoolchildren were to receive their first communion here this morning. If it had happened then it would have been a disaster," the local priest told Reuters.
A 14th Century mediaeval castle in the town of San Felipe Sul Pan was badly damaged, sparking alarm that one of its towers could topple.
The initial tremor - the strongest to hit Italy in three years - shook the major towns of Bologna, Modena, Ferrara, Rovigo, Verona and Mantua.
It lasted around 20 seconds and was felt throughout the northeast of the peninsula, from the Emilia-Romagna region to Venice, with its epicentre at Finale Emilia, 36 kilometres (22 miles) north of Bologna, the US Geological Survey said.
It was followed by a series of strong 5.1 magnitude aftershocks.
Mathew Hatton, who lives in Modena, was in a bar when the quake struck and everyone was forced to run out of the building.
He told Sky News: "There were a few people crying, some car alarms going off... it was quite a strong one.
"We saw a bit of confusion, people running around. It was a strange experience."
The region shaken by the quake is Italy's industrial heartland but also home to priceless architectural and art treasures. The historic centre of Ferrara is classified as a world heritage site.
"We were very afraid. All the village went out into the street after the first shock. After the second, many took shelter in their cars, but fortunately the damage was fairly limited, above all affecting churches," Umberto Mazza, the mayor of Ostiglia, near Mantua, told Italian news agency Ansa .
As dawn broke over the region, residents milled about the streets inspecting the damage.
Earlier, a 4.1-magnitude quake shook the Lombardy region around Milan, Italy's financial and business capital, and was felt in the historic cities of Modena, Mantua, Ferrara and Rovigo.
The last major earthquake to hit Italy was of 6.3 magnitude in the central Italian city of L'Aquila in 2009, killing around 300 people.
In January, a 5.3 magnitude quake in northern Italy was felt in Genoa, Bologna, Turin and Italy's financial capital, Milan.
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