Italian Prime Minister Matteo Renzi on Tuesday vowed to rebuild the entire region flattened by Sunday's earthquake as the country's main farming union called for help.

Speaking from Preci in the mountainous central region of Italy that has been devastated by three powerful tremors in just over two months, Renzi warned it would take time.

"I'm here to say that it won't be easy, it will take a long time... but little by little everything will be rebuilt," Renzi told villagers in Preci.

He had already pledged to rebuild every affected home while Culture Minister Dario Franceschini has promised every damaged fresco would be pieced back together.

Sunday's 6.6-magnitude earthquake, whose epicentre was near the mediaeval town of Norcia, which is famed for its ham and salami, was the most powerful to strike the country in 36 years.

Although it did not cause any deaths, it left some 22,000 people homeless with authorities putting them in hotels and holiday resorts on the Adriatric coast which are vacant now that the tourist season is over.

Thousands of homes have been left in ruins, with many villages and small towns rendered unsafe.

The quake also damaged a number of architectural landmarks, including the Abbey of Sant'Eutizio, one of the oldest monastic sites in Italy.

And it left around 3,000 farms in the region in urgent need of help, Italy's main farming union Coldiretti said on Tuesday.

- 100,000 animals may starve -

Farming is the primary industry in the mountainous region, which relies heavily on agriculture and agritourism, with the quake leaving 100,000 animals -- mostly cows, pigs and sheep -- now in danger of starving.

"The earthquake has hit hard in an area dominated by agribusiness with a significant amount of livestock farming which must receive concrete help so as not to be abandoned and depopulated," said Coldiretti president Roberto Moncalvo.

Many farmers are refusing to leave their farms because they don't want to abandon their livestock.

Significant numbers of farmers are struggling to find food and water for their herds, the union said, while damage to roads in remote areas is preventing them from delivering goods, including dairy products.

Coldiretti has provided caravans to some of those forced to leave their farms to enable them to stay close to their livestock.

Norcia itself has been left almost abandoned, barring a few stubborn and hardy souls, as thousands of residents sought refuge with friends and family or were bused to hotels on the Adriatic coast or on the inland Lake Trasimeno.

Overnight, a dog was pulled alive from the rubble of one of the houses in the village, which was just six kilometres (3.7 miles) from the epicentre of Sunday's quake.

- Earth moved by 70cm -

On Monday, Renzi said shipping containers would be used as temporary housing.

Meanwhile, Italian scientists said that areas hit by Sunday's temblor displaced the ground by up to 70 centimetres (27.5 inches).

Satellite images showed that the quake had deformed the landscape over an area covering some 130 square kilometres (50 square miles), Italy's National Research Council said in a statement.

The biggest displacement was in the Castelluccio region, near Norcia, where the ground was pushed up or sank by up to 70cm.

The quake struck at a very shallow depth and was followed by around 1,100 after-shocks, including 19 quakes registering between four and five magnitude and 240 of between three and four magnitude, the National Institute of Geophysics and Volcanology said.