Rescue workers raced against time to find survivors from an earthquake that struck central Italy Wednesday, as the death toll reached at least 159.

"It is a pain without limits," Prime Minister Matteo Renzi said during a visit to the earthquake zone.

National civil protection chief Fabrizio Curcio told Italian media 159 people were confirmed killed in the quake.

It is feared the death count could rise further. Many victims remain trapped under rubble, and dozens of people are still missing with hopes of finding them alive fading.

A total of 368 injured and sick people were rescued from the two worst-hit villages, Amatrice and Accumoli, after the earthquake of a magnitude of at least 6 struck the regions of Umbria, Lazio and Le Marche at 3:36 am (0136 GMT).

More than 1,500 people were left homeless in Le Marche alone, the ANSA news agency reported.

Italy was now standing together in solidarity to overcome the great challenges it faces after the quake, Renzi said.

"We will leave nobody on their own," Renzi pledged as he thanked people - including many who had searched for survivors with their bare hands - for aiding the rescue effort.

State broadcaster RAI reported 112 people killed in Amatrice alone.

Amatrice Mayor Sergio Pirozzi told ANSA many were still trapped under the rubble. "We're preparing a spot for the bodies," he said.

One focus of the town's fears was the historic Hotel Roma, which collapsed with as many as 70 guests inside, according to state broadcaster RAI.

Amatrice's hospital was evacuated, and its 15 patients were moved out into the street. People injured from the earthquake were also taken there.

Federico Rocchi, a student in his 20s, told dpa that Amatrice was completely destroyed.

"This is a town that is dead," Rocchi said, adding he had lost many friends.

Resident Eraldo Di Giacomo spoke of major devastation: "Everything has collapsed, houses, everything," he said in an interview with RAI. "Everything is broken."

In a few signs of hope, a boy was pulled alive from the rubble in the town of Pescara del Tronto, and a 6-year-old boy was freed from the rubble in Amatrice, though his twin brother remained missing, ANSA reported.

Rescue work was made more difficult by the region's mountainous terrain.

The European Union offered whatever aid it could provide, including access to satellite navigation services to better survey the scene.

"We stand, as ever, in solidarity with the Italian nation and are ready to assist in any way we can," European Commission President Jean Claude Juncker wrote on Twitter.

Italian President Sergio Mattarella appealed for solidarity during a "moment of pain and of appeal to common responsibility."

"The immediate need is to engage all forces to save lives, care for the wounded and ensure the best conditions for the displaced," he said.

US President Barack Obama called Mattarella to offer US condolences and support.

Pope Francis said he was nearly at a loss for words.

"Hearing the mayor of Amatrice saying that the town doesn't exist any more and knowing that there are children among the victims has moved me deeply," he said.

German Chancellor Angela Merkel also reached out.

"In the face of the extreme suffering and the massive destruction I would like to convey to you the deep sympathy of the German people," Merkel wrote in a condolence telegram to Renzi.

The quake was felt as far away as Rome, which lies about 150 kilometres south-west of the epicentre in the province of Rieti.

It was followed by more than 250 aftershocks, the National Institute for Geophysics and Vulcanology said, the strongest a 5.4-magnitude quake at 0233 GMT.

The disaster is not far from the city of L'Aquila, where a 5.9-magnitude quake killed 309 people seven years ago. However, there was hope that the death toll would be lower Wednesday, as the worst-struck areas were less populated than L'Aquila in 2009.

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