The head of the Italian Red Cross, Francesco Rocha, said 20,000 people were homeless and it could be months or even years before they were all back in their own homes.
More than 10,000 buildings have been destroyed - mostly in L'Aquila.
As rescue efforts continued:
A 98-year-old woman was pulled out alive in L'Aquila after being trapped for 30 hours, local media report. She spent the time crocheting
Four students have been located in a collapsed university hall of residence, but remain trapped under large chunks of masonry, the Associated Press reports. It is not known whether they are alive or dead
A 23-year-old student was pulled alive with the help of specialist cavers from the rubble of a four-storey building in L'Aquila more than 22 hours after the quake struck
L'Aquila and the surrounding area were without water
Latest from Dominic Hughes in Fossa, a village near L'Aquila
Successes are becoming rarer. At two o'clock this morning a woman was rescued by a team of expert cavers after a long and painstaking operation to remove huge slabs of concrete.
But with every passing hour the likelihood of finding survivors is reduced.
Apart from the search for survivors the most urgent task is to find some kind of accommodation for thousands of people who are now unable to return to their damaged homes.
Earlier Mr Berlusconi, appearing at a news conference in L'Aquila, thanked all involved in the rescue effort.
"There have been serious risks for the lives of those who are carrying out the rescue operation so far, inside buildings that have been damaged and, following another tremor, could easily collapse," he said.
"So therefore this is a very dangerous situation for the rescuers."
He said that starting from Wednesday specialists would start checking individual buildings.
Quake woman saved after 42 hours
Mr Berlusconi has refused foreign aid, saying Italians were "proud people" and had sufficient resources to deal with the crisis.
But AFP news agency quoted him as saying he could accept funds from Washington to help restore historical buildings.
Between 3,000 and 10,000 buildings are thought to have been damaged in L'Aquila, making the 13th-Century city of 70,000 uninhabitable for some time.
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