Cuba says it was generating only enough electricity to cover about one-sixth of peak demand late on Wednesday, hours after its national grid collapsed leaving millions without power.

The National Electric Union (UNE) said it was producing 533 megawatts of electricity by evening, still just a fraction of typical dinnertime demand of between 3,000 and 3,200 megawatts, leaving most Cubans in the dark as night fell across the Caribbean island.

Earlier, the communist-run government said it would prioritize returning power to hospitals and water pumping facilities. Schools and non-essential government services were closed until further notice.

Lights flickered on across parts of the capital Havana late on Wednesday. The local electric company said more than 260,000 clients had seen power restored.

It was the latest in a string of countrywide blackouts of Cuba's antiquated and increasingly frail power generation system. This year, Cuba's grid fell into near-total disarray, stressed by fuel shortages, natural disaster and economic crisis.

Dwindling oil imports from Venezuela, Russia and Mexico pushed the island's obsolete and struggling oil-fired power plants into full crisis several months ago.

Hours-long rolling blackouts and severe shortages of food, medicine and water have made life increasingly hard for many Cubans, who in recent years have fled the island in record-breaking numbers.

Cuba blames U.S. sanctions, which complicate financial transactions and the purchase of fuel, for the crisis.

Blackout triggered by power plant failure

The Wednesday morning blackout was triggered by a failure at the Antonio Guiteras power plant in Matanzas, which shut down around 2 a.m. local time.

Several other major power plants were undergoing maintenance and were offline when the Matanzas plant failed, starving the grid of electricity and leading to the countrywide collapse, the energy minister said.

WATCH | Cubans protest October power failures:

Frustrated Cubans protest persistent power failures

Residents of Havana took to the streets Monday night to demand something be done about the ongoing blackouts after the country's power grid failed multiple times, leaving the nation in darkness.

Havana hotel worker Danielis Mora woke up frustrated and confused, like many Havana residents who now experience regular blackouts.

"I didn't know it was a total blackout again," Mora said. "Where I am living ... there is no gas either, if there is no electricity there is no way to make food, it has to be with firewood or charcoal."

Scattered protests have erupted over the past two months over the repeated power failures as well as water, gas and food shortages.

Cuba's decrepit and long obsolete grid collapsed multiple times in October as fuel supplies dwindled and Hurricane Oscar struck the far eastern end of the island, then again in November with the passage of Hurricane Rafael.

Cuba's government last week issued a decree ordering state and private businesses to generate more of their own electricity from renewable resources.

The regulations also require businesses to limit their use of air conditioning — among other measures — as the country wrestles with the increasingly dire energy crisis.