A new earthquake has struck the Emilia region in northern Italy, killing at least 15 people and leaving several others trapped under rubble.
Tuesday’s tremor, estimated at magnitude 5.8, hit the same region where a quake 10 days ago killed seven people and destroyed many buildings.
The Italian government says the number of people made homeless has gone up from 6,000 to 14,000.
Prime Minister Mario Monti has pledged to help all those affected.
The towns of Mirandola, Medolla and Cavezzo were closest to the epicentre but the northern cities of Milan and Bologna were shaken too.
The quake struck 40km (25mi) north of Bologna and 60km east of Parma, at a depth of 9.6km (six miles), Reuters reports. It was felt as far away as Venice and the Austrian border.
Many people ran out of buildings when they felt the tremor, which hit at 09:03 local time (07:03 GMT).
There have been several aftershocks since, including a large one at about midday which sent people out into the streets in cities up to 100km away, the BBC’s Mark Duff reports from northern Italy.
In Pisa, offices were evacuated as a precautionary measure while there were moments of panic in Venice, where a statue fell to the ground.
Pictures have been emerging from the worst-affected areas, showing factories and office blocks reduced to rubble.
Firemen with dogs are trawling through what remains of the buildings for survivors.
Among the dead were four people in Mirandola, including two who were in a factory that collapsed. Three people also died in San Felice, and two in Cavezzo, some 30km (20mi) from Modena.
The Corriere della Sera news website says three people were killed at a factory that had only been cleared for re-entry on Monday, following the first earthquake.
A parish priest in the town of Rovereto di Novi is reported to have been killed by a falling beam when he went back into his church to save a Madonna statue.
Many historic buildings now lie in ruins in Cavezzo, where the roof of a church damaged by the earlier quake collapsed on Tuesday, Il Messaggero news website reports.
Calls to emergency services have overloaded the telephone network in some areas, causing a system blackout. Train services have been halted in some parts of northern Italy.
‘A feeling of waves’
An emergency cabinet meeting is scheduled for Wednesday. Troops stationed in Bologna have been sent to the affected areas.
Prime Minister Mario Monti said: “I would like to assure everyone that the Italian state will do everything we must do and is possible to do in the shortest possible time to guarantee a return to normal life in this area, that is so special, so important, so productive for Italy.”
Chris Brewerton, living in Mantua, told the BBC that Tuesday’s quake appeared stronger than the one on 20 May, which was 6.0 in magnitude. Mantua is 58km (36 miles) north of Modena.
“The chair starts shaking and there’s a feeling of waves below me,” he said. “I rush out into the garden; the shutters and garage door are banging, the ground below me swaying. It lasted about 15 seconds – it was frightening.”
A Londoner living in Modena, Christopher Gilbert, said he felt “a rolling earthquake lasting around 15 seconds – people were quite frightened.
“I was having a coffee when the quake struck and felt a swaying motion so I clutched onto a bar in the cafe to steady myself. Schools and offices were evacuated,” he told the BBC.
A friendly match between Italy and Luxembourg ahead of the Euro 2012 football championships, due to be played in the northern city of Parma on Tuesday, has now been called off.
The 20 May quake destroyed many centuries-old buildings of cultural value. It was the worst to hit Italy since the L’Aquila tremor that killed nearly 300 people in 2009.