Cuba's power grid has ground to a halt for a second time in as many days, leaving 10 million on the island without power and the Caribbean island in a growing sense of crisis.

Cuba's power-grid operator said it had restored electricity to parts of the capital Havana on Monday following a fourth major grid failure in 48 hours, while Tropical Storm Oscar lashed the island's eastern end.

Tropical Storm Oscar doused Cuba on Monday, three days after a massive power failure plunged more than 10 million people into the dark as the island worked to restore its decades-old power grid.