A powerful earthquake in mountainous central Italy knocked down whole blocks of buildings early on Monday as residents slept, killing at least 50 people and trapping many more, officials said. Thousands were homeless.

The earthquake's epicentre was about 110 kilometres northeast of Rome near the medieval city of L'Aquila. It struck at 3:32 a m local time (0702 IST) in a quake-prone region that has had at least nine smaller jolts since the beginning of April.

US Geological Survey said the quake was magnitude 6.3, but Italy's National Institute of Geophysics put it at 5.8.

Interior Minister Roberto Moroni, arriving in L'Aquila hours after the quake, said 50 people had been killed.

Officials said the death toll was likely to rise as rescue crews clawed through the debris of fallen homes.

L'Aquila Mayor Massimo Cialente said some 100,000 people had left their homes and that many buildings in the city's historic centre were damaged. Slabs of walls, twisted steel supports, furniture and wire fences were strewn about the streets and a gray dust carpeted sidewalks, cars and residents.

As ambulances screamed through the city, fire-fighters aided by dogs worked feverishly to reach people trapped in fallen buildings, including a student dormitory where half a dozen university students were believed still inside.