Russian attacks left Ukraine's southeastern regions of Dnipropetrovsk and Zaporizhzhia almost entirely without power, the country's energy ministry said on Wednesday night.
Critical infrastructure was "operating on reserve power", it said in a statement on Telegram, while officials said water supplies and the internet were also disrupted.
Russia has recently intensified attacks on Ukraine's energy infrastructure, aimed at paralysing power supplies during a harsh winter.
"Ukraine's energy system is under enemy attacks every day, and energy workers are operating in extremely difficult conditions to provide people with light and heat," Ukraine's Prime Minister Yulia Svyrydenko wrote on Telegram.
"Deteriorating weather conditions put additional strain on critical infrastructure," she said.
