* Electricity went off in Kenya, Uganda early on Saturday
* Uganda also experiencing loadshedding
* Power restored in most of Kenya (Adds power restored in most of Kenya)
By Elias Biryabarema and George Obulutsa
NAIROBI/KAMPALA, May 9 (Reuters) - Kenya and Uganda were hit by power blackouts on Saturday, and Kenya Power said the outage on its grid was caused by a fault on a high voltage line but that it had restored supply to most parts of the country.
The neighbouring East African countries' grids are interconnected. In January 2018, both suffered major blackouts due to what they said were system disturbances.
Kenya Power, with 7 million customers on its grid, said electricity went off at 5:49 a.m.(0249 GMT).
It said in a statement it said its engineers had identified a fault on a section of a high voltage power line that transmits power to Nairobi from the Olkaria geothermal power plants, some 75 km (45 miles) from Nairobi.
"The fault ... led to power loss on the critical power line thus overloading the other power generators countrywide and is suspected to have caused the outage," Kenya Power said.
Kenya Power said later on Saturday that in addition to Nairobi, electricity supply had been restored to most parts of the country, including all other major cities and towns.
The Uganda Electricity Transmission Company 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."
Ugandan power distributor Umeme Ltd had said on Friday there would be loadshedding for eight hours daily between Saturday and Monday while the Uganda Electricity Transmission Company conducted water release tests on four major hydroelectric power plants.
The plants are Nalubaale, with 180 MW installed capacity, Kiira with 200 MW, Bujagali with 250 MW and Isimba with 183.2 MW.
Uganda's water and environment minister Sam Cheptoris said in late April that water levels of Lake Victoria had risen to levels last recorded in 1964 and were a threat to those four major dams.
On April 14, Uganda also had a nationwide power outage after weeds clogged Nalubaale, Kiira and Bujagali, causing them to trip.
Uganda's power grid reaches about 25% of the population according to the energy ministry. (Additional reporting by Duncan Miriri in Nairobi; Editing by Alex Richardson)
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