Italy's strongest earthquake in decades rocked central parts of the country early Sunday, toppling buildings and forcing closure of the subway system in Rome more than 100 miles away.

The United States Geological Survey said the magnitude-6.6 quake struck at about 7:40 a.m. local time (2:40 a.m. ET) and was centered in Norcia, a town of 5,000 people. Norcia is only about 35 miles from Amatrice, a town devastated by a quake two months ago. The area was also hit by temblors last week that left thousands homeless.

Fabrizio Curcio, head of Italy’s Civil Protection Agency, said early reports indicated about 20 people suffered injuries, none life-threatening.

The earthquake was more powerful than the 6.2 quake that struck Italy in August, killing nearly 300 people and destroying parts of Amatrice and other historic towns. Many people in the mountainous region, located along a fault line, have been sleeping cars or temporary shelters, afraid their homes could collapse in the night amid the continuing seismic activity.

In Norcia, unconfirmed reports in Italian media said that at least nine people had been pulled alive from the rubble. Buildings were damaged and emergency workers were continuing to check for casualties. However, the USGS said Sunday's quake was registered at a depth of less than a mile — a distance that is considered extremely shallow and might mean that the destruction could be relatively limited.

"We are trying to understand if people are under the rubble," said Cesare Spuri, the regional head of Italy's civil protection authority.

Marco Rinaldi, the mayor of the nearby village of Ussita, said there was severe destruction in his area. "Everything collapsed. I can see columns of smoke, it's a disaster, a disaster," he told Italy's ANSA news agency.

"I was sleeping in my car, I saw hell break out," Rinaldi said.

An international community of Monks in Norcia, an ancient town about 100 miles northeast of Rome and known for its Benedictine monastery, tweeted an image of the 14th century St. Benedict cathedral with only its facade standing.

Extremely strong tremors were felt as far away as Rome, where the historic Basilica of St. Paul Outside the Wall was closed due to the appearance of large cracks in the ceiling. Italy's civil protection department said it was checking all the towns affected by the quake. Italy's Red Cross said that its emergency centers were activated across the country.

The latest quake came after temblors in Italy last week left thousands homeless. The last time Italy experienced an earthquake as strong as Sunday's was in 1980, when a magnitude-6.9 quake left more than 2,400 dead and injured 7,700. Tens of thousands of people lost their homes in that disaster.