Cuba has completely run out of diesel and fuel oil, Energy Minister Vicente de la O Levy told state media. The country's energy system is in a "critical" state as a US-led blockade tightens supply.
Scattered protests against power cuts broke out in Havana on Wednesday. Blackouts have lasted up to 22 hours in parts of the capital.
Hospitals are struggling to operate. Schools and government offices have closed. Tourism, a key economic driver, has also been hit.
Cuba normally depends on Venezuela and Mexico for oil. But both countries have largely cut supplies since President Trump threatened tariffs on fuel shipments to Cuba.
The US has offered $100 million in humanitarian aid, delivered through the Catholic Church, in exchange for political reforms. Cuba's Foreign Minister Bruno Rodriguez called the conditions "illegal and abusive."