The electricity outage was caused by a technical fault, power utility Tanesco.
Power has been restored in Tanzania after a massive nationwide blackout that affected several islands and most of the mainland on Monday.
The electricity outage struck shortly after 02:00 local time on Monday, privately owned newspaper Daily Citizen reported.
State-run power company Tanesco said the outage was caused by a technical fault at the Kidatu hydroelectric power plant in the east of the country.
Its water intake control equipment was affected.
The fault resulted in large volumes of water entering the systems, causing them to “suddenly shut down to protect themselves”, and in turn impacting the national power grid, Tanesco added.
Energy Minister Doto Mashaka Biteko ordered power officials who were on their Easter break to return to work immediately in order to restore power supplies.
On Monday evening, Tanesco said it had restored power to most parts of the country, although several Tanzanians continued to complain of outages on social media.