A failure in a main transmission line in central Cuba caused a blackout that cut electricity for several hours to more than half the country on Sunday night, the government said on Monday.
The Ministry of Basic Industry said in a statement there was an "interruption" in a 220,000-volt line between the cities of Ciego de Avila and Santa Clara, which caused a power outage that stretched more than 450 miles (725km) from Camaguey in the south-east to the westernmost province of Pinar del Rio and included the capital Havana.
It said the cause of the transmission line failure was being investigated.
The ministry did not say how many people were affected, but Cuba has a population of 11 million.
The power went out just after 8pm and was restored in much of the affected area within a couple of hours, but the outage lasted almost five hours in Havana where off-duty officers were called in to direct traffic in the dark streets with no functioning traffic signals.
It appeared to be fully restored on Monday morning, although officials had not confirmed that.
Blackouts are not uncommon in Cuba due to its aging electrical system.
This one was more extensive than most and reminded some of the so-called 'Special Period' in the 1990s when the country faced severe energy shortages following the collapse of the Soviet Union, its top benefactor.
Cubans said they did what they did during the long, frequent outages of those days -- close up shop if they were in a retail establishment or just find a cool place and go to sleep.
"We stopped sales, collected the goods and put up a guard to avoid any crime," said restaurant worker Rodolfo Garcia.
"I opened the door [to my house], laid down on the floor and went to sleep," said Dianelys Carrera, an employee at a Havana convention centre.
Cuba is heavily dependent today on Venezuela, whose President Hugo Chavez provides two-thirds of the country's oil under highly favourable terms in an oil-for-services deal.
Chavez has been treated for cancer the past year in Cuba and is running for re-election next month.