A nationwide blackout that hit Kenya yesterday was caused by a monkey tripping a transformer at a hydropower plant, leading to the loss of more than 180 megawatts from the grid, power producer Kenya Electricity Generating Company (KenGen) said.

Power distributor Kenya Power and KenGen said electricity supply was knocked out at 11.30 am local time after a technical fault at Gitaru Hydro power station.

KenGen, the East African country's biggest power producer, runs the station.

"A monkey climbed on the roof of Gitaru Power Station and dropped onto a transformer tripping it. This caused other machines at the power station to trip on overload resulting in a loss of more than 180 MW from this plant which triggered a national power blackout," KenGen said in a statement late on Tuesday.

"KenGen power installations are secured by electric fencing which keeps away marauding wild animals. We regret this isolated incident and the company is looking at ways of further enhancing security at all our power plants."

Kenyan businesses regularly complain that power cuts - due to its ageing grid - and unreliable supplies make them uncompetitive and hurt growth.