Cuba’s electrical grid went offline Friday after one of the island’s major power plants failed, and as a massive blackout that started a day earlier swept across the Caribbean island.

Cuba's energy ministry announced that the grid had gone down hours after the Antonio Guiteras thermoelectric plant had ceased operations, at about 11 a.m. local time. Authorities said at the time it was only offline temporarily.

Hours earlier, Prime Minister Manuel Marrero had sought to assuage concerned citizens about the outage that began Thursday evening. Millions of Cubans were left without power, prompting the government Friday to implement emergency measures to slash demand, including suspending classes, shutting down some state-owned workplaces and canceling non-essential services.

Various calls by The Associated Press seeking to clarify the extent of the blackout on Friday weren’t answered. In addition to the Antonio Guiteras plant, Cuba has several others and it wasn’t immediately clear whether or not they remain functional.

“We are devoting absolute priority to addressing and solving this highly sensitive energy contingency," Cuba's President Miguel Díaz-Canel wrote on X. “There will be no rest until its restoration.”

Cuban officials earlier said that 1.64 gigawatts went offline during peak hours early Thursday evening, about half the total demand at the time.

“The situation has worsened in recent days,” Marrero said in a special address on national television in the early hours of Friday. “We must be fully transparent ... we have been halting economic activities to ensure energy for the population.”

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During his address, Marrero was accompanied by Alfredo López, the chief of UNE, who said the outage stemmed from increased demand from small- and medium-sized companies and residences’ air conditioners, as well as breakdowns in old thermoelectric plants that haven’t been properly maintained and the lack of fuel to operate some facilities.

Changes to electricity rates for small- and medium-sized companies, which have proliferated since they were first authorized by the communist government in 2021, are also being considered, Marrero said.

Marrero sought to placate people’s concerns about the outage, citing an expected influx of fuel supply from Cuba's state-owned oil company.

Even in a country accustomed to frequent outages amid a deepening economic crisis, the size of Thursday night’s blackout left millions of Cubans on edge. Residents shut their doors and windows they typically leave open at night, and candles or lanterns were visible inside their homes.