Power was restored in Cuba early Monday after a massive outage caused by a malfunction in a high voltage power line cast much of the country into darkness for hours.

The blackout, which began at 10: 08 p.m. local time (0008 GMT Monday), hit 10 of Cuba 's 15 provinces, including Havana . Six provinces went totally dark for three hours, the state-run Electric Union company said.

It said it was caused by a malfunction on a high-voltage line between the cities of Ciego de Avila and Santa Clara , disrupting service from the eastern province of Camaguey to Pinar del Rio at the western end of Cuba .

Residents said Pinar del Rio , Artemisa, Havana , Mayabeque, Matanzas and Cienfuegos were left completely without electricity.

The cause of the malfunction was under investigation, the company said.

The situation in the capital -- where more than two million of Cuba 's 11 million people reside -- remained calm, although the police presence on some streets had been noticeably beefed up.

Many people in Havana left their homes to spend the night in the open because they could not use fans or air conditioning, and the heat inside -- about 30 degrees Celsius (near 90 degrees F) -- quickly became unbearable.

After three hours, electricity began to return to some areas of Havana but others remained in the dark.

In Cienfuegos , the blackout lasted about an hour, residents said.

While rolling blackouts to save energy are not unusual in cash-strapped Cuba , a broad failure of the power grid like this is rare.

Energy shortages are the Achilles heel of Communist-run Cuba 's economy, which for more than a decade has been propped up by subsidized oil from ally Venezuela .

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