A desperate search for survivors is on in the mountain city of L'Aquila in central Italy after a quake killed at least 90 people and injured 1,500.
Rescuers are picking through rubble in the walled medieval city and nearby towns and villages, some of which are said to have been virtually destroyed.
Tents are being put up in tennis courts and on football pitches to house some of the 30,000-40,000 homeless.
Italy's PM Silvio Berlusconi promised a "record number of rescuers".
See map of the earthquake-hit area
Earlier, he declared a state of emergency in the region.
Gianfranco Fini, speaker of the lower house of parliament, told MPs: "Some towns in the area have been virtually destroyed in their entirety."
The 6.3-magnitude quake struck at 0330 (0130 GMT) close to L'Aquila, 95km (60 miles) north-east of Rome.
It lasted about 30 seconds, bringing down many Renaissance-era and Baroque buildings, including the dome on one of L'Aquila's churches.
Boulders fell off mountain slopes, blocking roads. Houses were reduced to piles of rubble and cars crushed by raining debris.
One resident, Antonio di Marco, recounted his experience for the BBC: "We escaped outside like madmen, we didn't understand what was happening, the whole building was moving under our feet, it is something that's impossible to describe…"
"It's a catastrophe and an immense shock," resident Renato Di Stefano told the Associated Press as he and his family headed for shelter in a tent camp outside L'Aquila.
"It's struck in the heart of the city, we will never forget the pain."
Fire-fighters aided by dogs worked feverishly to reach people trapped in fallen buildings in L'Aquila, including a student dormitory where several students were believed to be still inside.
Here in the centre of the city, building after building has been left destroyed or half standing with cracks and holes.
We watched as rescue workers struggled to pull out survivors, crawling on their stomachs to try to reach those trapped inside.
There is a stream of almost ghostly figures, local people caught up in the early hours this morning in this earthquake, who are pouring past us wearing blankets.
They are pulling suitcases and luggage past this collapsed building trying to get to safety. People are wandering around in a dazed state.
Earlier, residents and rescuers used their bare hands to clear the debris from collapsed buildings.
Mr Berlusconi, who is in L'Aquila, said a field hospital was being set up to help local medical services.
"I can assure you that there is no building that has fallen down without rescuers, without fire brigade being there," he told reporters after arriving in the city.
Italy, he said, had the resources it needed to deal with the disaster: "Financially, there are no problems. The government has all the necessary funds at its disposal. We also have the EU catastrophe fund."
Officials say 26 cities and towns have been damaged in the region, not including villages and hamlets.
The BBC's Duncan Kennedy in L'Aquila has described bemused and confused locals wrapped in blankets and carrying their personal belongings in suitcases walking, like a stream of refugees, through the devastation.
The rescue service is stretched to breaking point as it tries to reach all the devastated buildings and care for the survivors and the homeless.
Race against the clock
Survivors, some still in their night clothes, hugged each other as they waited for news of friends and relatives on Monday morning.
A rsecuer with his dog in Onna, 6 April
Sniffer dogs were being used to check rubble in Onna, just outside L'Aquila
Hundreds waited at the city's main hospital, where doctors were forced to treat people in the open air because only one operating room was functioning.
Francesco Rocca of the Italian Red Cross warned of the difficulties ahead.
"The biggest problem will arrive in the night because there are thousands and thousands of people that we have to host in tents, in the hotels," he told the BBC.
Deaths were reported in the surrounding towns and villages of Castelnuovo, Poggio Picenze, Tormintarte, Fossa, Totani and Villa Sant'Angelo.
In the small town of Onna, 10 people were killed, said a Reuters photographer who saw a mother and her infant daughter carried away in the same coffin.
MAJOR ITALIAN QUAKES
2002 - 30 die, including 27 pupils and their teacher, in the southern town of San Giuliano di Puglia
1997 - 13 die and priceless cultural heritage lost in the central Umbria region
1980 - Nearly 3,000 people die, some 9,000 injured and 30,000 displaced near Naples
Phone and power lines have been down and some bridges and roads have been closed as a precaution against aftershocks.
Italy lies on two fault lines and has been hit by powerful earthquakes in the past, mainly in the south of the country.
World leaders have sent messages of condolence and Pope Benedict XVI offered prayers for the "victims, especially the children".
The EU, Austria, France, Germany, Greece, Israel and Russia immediately stepped forward with offers of aid, if required.