Pockets of Cuba's capital Havana saw the lights flicker back on though vast areas of the city and country continued without electricity on Sunday morning, after a nationwide grid collapse that knocked out power to 10 million people.

The collapse follows nationwide blackouts last year that plunged Cuba's frail power-generating system into disarray.

The grid failed on Friday evening about 8:15pm (00:15 GMT) after a breakdown at Diezmero substation in the capital, Havana, kicked off a chain reaction that shut down power generation across the island, according to officials at operator Union Electrica (UNE).