The power outage occurred on Wednesday morning, and the entire power grid was shut down, according to the country's energy department.
A possible cause, according to the department, was that the Antonio Guiteras power plant was suddenly shut down - and affected the power grid.
Cuba has recurring problems with power outages due to system failures or fuel shortages, as the country's currency reserve is minimal and the country lacks assets to buy energy for.
Often the power outages are regional, but the national power outages are becoming more frequent.
