A failure at one of Cuba's major power plants resulted in island-wide blackouts on Friday, the communist nation's Ministry of Energy and Mines said. 

The electric system at the Antonio Guiteras thermoelectric plant was "completely disconnected" at 11 a.m., the agency said on X. The failure left millions of Cubans without power in a country used to frequent power outages amid a seeping economic crisis. 

The energy agency said it was working to restore power. 

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Cuban officials said that the blackout, which started late Thursday, saw 1.64 gigawatts go offline during peak hours in the early evening, about half the total demand at the time.

"The situation has worsened in recent days," Prime Minister Manuel 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."

"From the highest leadership of the country we are working to resolve this energy contingency as soon as possible," he later wrote on X. "We will not rest until it is restored."

During his address, Marrero was accompanied by Alfredo López, the chief of the state-owned utility 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.

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The communist-run government earlier in the day shut down schools and non-essential industries. Most government workers were sent home in an effort to conserve energy.

The Associated Press contributed to this report.