An outage at the Diezmero substation on the outskirts of Havana had caused “a significant loss of generation in western Cuba and, with it, the failure of the National Electric System.”

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.