Hurricane Oscar left six people dead after hitting Cuba over the weekend during a major power blackout, authorities said on Monday, as electricity was restored to most of the capital.

The lights went out for the country's 10 million people on Friday after the collapse of the nation's largest power plant crippled the whole grid.

By Monday afternoon, nearly 90 percent of customers in Havana – home to some two million people – had power again, the capital's electricity company said in a report published by state-run news portal Cubadebate.

"Of course I'm happy!" Olga Gomez, a 59-year-old housewife in Havana, said after the lights came back on.

"I have an elderly senile mother of 85 and an autistic son. It's very difficult when there's no power," she said.

Many residents outside Havana, however, remained without electricity, according to the authorities.

Cuba was still bathed in darkness on Sunday when Hurricane Oscar made landfall in the eastern part of the country as a Category 1 storm, causing several deaths and damage.

"Regrettably, according to preliminary information, six lives have been lost," President Miguel Diaz-Canel said in a televised remarks.

The storm caused severe damage in the eastern province of Guantanamo, he said.

Oscar weakened into a tropical storm as it moved inland but was still expected to bring "significant, life-threatening flash flooding along with mudslides," the US National Hurricane Center warned.

Roofs and the walls of houses were damaged, and electricity poles and trees felled, state television reported. (AFP)