HAVANA (AP) — After a nationwide blackout left millions without electricity for several hours in Cuba, the power grid was restored Thursday, authorities said, adding that scheduled power outages will now resume.

The latest blackout, the third one of this severity in less than two months, occurred in the early hours of Wednesday, after a breakdown at a thermoelectric plant in Matanzas province, east of Havana. The incident triggered a chain reaction, overwhelming an already strained power system.

On Thursday, classes and work activities gradually returned to normal.

As for the scheduled power outages, Cuban authorities said they will continue their current practice of implementing daily, five-hour power outages by block or zone as they have been doing for the past few months.

On Oct. 18, the island suffered a significant blackout that, added to the passage of Hurricane Oscar two days later, left the island without electricity for several days.

Weeks later, Hurricane Rafael’s strong winds triggered another system-wide blackout that left the national energy system disconnected again.

Cuba’s power grid has been plagued by frequent outages in recent months, with more than half of the country experiencing power cuts during peak hours. The outages are primarily caused by fuel shortages and aging infrastructure. In many parts of the island, electricity is crucial for cooking and water pumping.

Cubans have been grappling with several crises in rapid succession in the past three weeks after the island’s eastern region was hit Sunday with a powerful earthquake even as the country was still reeling from two hurricanes that brought death and devastation.

A 6.8 magnitude earthquake in the ocean 20 miles off Pilón, a town on the southern coast of the province of Granma in eastern Cuba, shook the region on Sunday minutes before noon, leaving no casualties but at least two children, among them a five-year-old, and two adults injured, Cuban state media said.

The strong tremor followed a magnitude 5.9 earthquake earlier on Sunday morning that the United States Geological Survey said occurred 21 miles south of the nearby municipality of Bartolomé Maso, also in Granma province.

Cuba’s National Center for Seismological Research reported Monday morning that it had detected 885 tremors – including the two biggest ones - in the area in the past 24 hours. Eastern Cuba is in an active seismic zone in the Caribbean that is responsible for most of the tremors felt on the island. In 2020, the Center reported a 7.7 magnitude earthquake west southwest of Cabo Cruz, in Granma province, but it happened at sea and did not cause damage.

The country’s leader, Miguel Díaz-Canel, urged residents in Granma to remain in open areas and follow earthquake protocols. Videos circulating on social media show panicked residents in Pilón left their houses Sunday to take refuge in the nearby mountains.

Cuban authorities have yet to provide a detailed assessment of the damage caused by the earthquakes However, images shared by state media and social media accounts show several collapsed homes, and houses, buildings and schools with cracks or crumbled walls.

Videos and photos show extensive damage in Pilón and cracks in the 1871 lighthouse in Cabo Cruz.

The earthquakes put additional strain on a population already dealing with multiple crises just days apart.

On the eve of Oct. 18, the government declared an energy emergency, citing a lack of oil and the diminished generating capacity of its old energy infrastructure as culprits of daily extended blackouts that had paralyzed the economy. The following morning a failure at a major power plant caused the entire electrical grid to collapse.