The mass blackout -- though attributable to a fire -- was one of many that have hit Ukraine's grid since Russia focused in October on attacking energy infrastructure as part of its invasion of Ukraine.
"Repair work is going on round the clock. The situation at this time is that hundreds of thousands of people in Odesa region are without power," Zelenskiy said in his nightly video address.
Zelenskiy said that such disruptions in Ukrainian cities "could not have happened" before the onset of Russian attacks on power generation sites over several weeks, some of which involved dozens of missiles at a time.
Zelenskiy did not say how long the repair works would take, but Ukrainian officials said earlier they could take weeks.
(Reporting by Ron Popeski and Nick Starkov; Editing by Lisa Shumaker)
