Cuba's efforts to restore power to the island were derailed for a third time late on Saturday, Cuban authorities said shortly before midnight, leaving millions in the dark and raising fresh questions over the viability of the government's bid to reestablish electrical service.

Cuba restored a trickle of power to its grid by mid-evening on Friday, officials said, hours after the island plunged into a countrywide blackout following the collapse of one of its major power plants.