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.

Cuba remains largely without power a day after the country's grid collapsed, raising fresh questions about the island's generating system; officials gave no timeline for restoring service.

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