A MAGNITUDE-6.4 earthquake has struck Puerto Rico and was followed three hours later by an aftershock measuring 6.0.

They are the largest in a series of quakes that have struck the US territory in recent days and caused heavy damage in some areas.

Eight people were injured in the city of Ponce, near the epicentre, mayor Mayita Melendez said.

Puerto Rico’s power authority said on Twitter that one of the country’s main power plants, which sits near the epicentre, had been damaged, but officials expect to restore power to the island later.

The US Geological Survey said the quake hit at 4.24am just south of the island at a shallow depth of 10km. It initially gave the magnitude as 6.6 but later adjusted it.

At 7.18am the magnitude-6.0 aftershock hit the same area. People reported strong shaking and staff at a local radio station said live on air that they were leaving their building.

A tsunami alert was issued for Puerto Rico and the US Virgin Islands after the initial quake, but was later cancelled.

The mayor of Guayanilla, Nelson Torres, told NotiUno radio station that the church in the public plaza of his town collapsed.

Victor Huerfano, director of Puerto Rico’s Seismic Network, said that it is hard to obtain reports of damage or injuries because communications are down for much of the island. He said officials in Ponce told him there was widespread damage.

“We expect that this will be the largest quake for now,” he said. “The aftershocks will continue for some time.”

Puerto Rico’s governor, Wanda Vasquez, told station Radioisla that there had been no immediate reports of deaths.