Teams from Kenya Power and Uganda’s power Distributor Umeme announced on Twitter that efforts to restore power were already underway.
The neighbouring countries’ grids are interconnected.
Kenya Power said power went off at 5:49 a.m. (0249 GMT).
“Our engineers are working to identify and address the hitch, towards restoring normal electricity supply,” it said in a statement.
Already the firm has restored power to certain parts of the country.
Kenya Power indicated that it had identified a technical fault at a section of the main high voltage transmission power line that evacuates power from the Olkaria geothermal power plants to Nairobi.
“An electricity conductor came off the support insulators and clashed on the towers,” the firm said in a statement.
Uganda also suffered a nationwide blackout, Uganda Electricity Transmission Co. Ltd said on its Twitter account.
“We have lost transmission across the nation … please bear with us as we investigate the cause and work on restoration,” it said.
Restoration of services is already ongoing in most parts. We shall update you once all power stations have been restored. |Fe
— Umeme Limited🇺🇬 (@UmemeLtd) May 9, 2020
In January 2018, both countries suffered major blackouts due to what they said were system disturbances.