The death toll in a strong earthquake in central Italy has risen to 21, authorities said Wednesday.

The magnitude-6.0 earthquake hit the city of Rieti at 3:32 a.m. Wednesday (0132 GMT), with a shallow depth of 4.2 km, according to the National Institute of Volcanology and Seismology.

Several powerful aftershocks followed, said the agency.

The temblor was strongly felt across the Lazio region and in Rome, the capital of the country.

Amatrice and Accumuli, two small towns in the Rieti province, were among the hardest hit, local media reported. Sergio Pirozzi, mayor of Amatrice, told local media that "most of the town is gone."

Five people were believed to have been killed in Amatrice and six were reported dead in the town of Accumuli, while 10 people, including an elderly married couple, died in Pescara del Tronto in the Marches.

"Unfortunately, we expect the number of victims to rise as day breaks," Accumuli mayor Stefano Petrucci said.

Rescue teams and citizens were at work in the early morning, digging to find survivors as voices of people trapped under rubble could be heard, Ansa news agency reported.

Italy's Civil Protection Agency described the earthquake as "severe."

Civil Protection chief Fabrizio Curcio told a press conference in Rome early Wednesday that the earthquake could be compared to the strong earthquake that hit the city of L'Aquila in 2009, which left more than 300 people dead and thousands displaced.