Strong earthquake slams northern Italy

The Italian prime minister, Mario Monti, who is in the United States for high-level meetings with leaders from the Group of 8 nations and NATO, said on Sunday that he would return to Italy ahead of time because of the emergency.

Many areas of Italy are considered to be at high risk for earthquakes. A quake in 1976 killed nearly a thousand people in Friuli Venezia Giulia, and almost 3,000 died in the Campania earthquake of 1980.

Three years ago, an earthquake in the area of L'Aquila, in central Italy, killed more than 300 people. While rebuilding has advanced in many villages in the region, the historic center of L'Aquila itself remains a ghost town and there has been public outcry over delays in reconstruction there.

But in Emilia Romagna, seismic events of this kind have been more rare. Gregori said that the last quake of this magnitude in the area was in the 14th century. "For man, seven centuries are a lot, for nature it is nothing," he said.

Aftershocks were felt in the region throughout Sunday. The main quake was felt throughout northern and central Italy, "for hundreds of kilometers, there was a considerable release of energy," said Stefano Gresta, a geophysicist and president of the National Institute of Geophysics and Volcanology.

Gresta said that aftershocks could continue for days, "and we can't even exclude a significant quake like the one this morning," he said.

On Sunday afternoon, another tremor, initially measured at a magnitude of 5.1 by the USGS, caused further havoc, felling other structures, and hampering the work of rescue teams.

Areas in some of the hardest-hit towns, scattered across a vast swath of Italy's agricultural heartland, were cordoned off while officials expressed concern about the stability of some historic buildings.