Ukraine was bracing for hours-long power cuts on Thursday after electricity lines were destroyed during a Russian bombardment.
President Volodymyr Zelenskyy said people should cut back their electricity use from 7am on Thursday.
Energy company Ukrenergo said power lines had taken more damage in the past 10 days than in the previous eight months as Russian increases its missile attacks.
Russia admitted to striking energy infrastructure with long-range missiles, while Ukraine said Iranian-made drones were also involved.
Controlled power cuts could last for up to four hours at a time after an estimated 30 per cent of Ukraine's energy infrastructure was damaged.
Officials said further power cuts could be needed in the coming weeks as the cold Ukrainian winter sets in.
People were urged to charge up their phones, torches and power banks before the lights go out.
“Please do not turn on unnecessary electrical appliances. Please limit your electricity consumption and use [of] those appliances that consume a lot of energy,” Mr Zelenskyy said in his nightly address.
“We assume that Russian terror will be directed at energy facilities until, with the help of partners, we ensure the ability to shoot down 100 per cent of enemy missiles and drones.”
Ukraine is pleading for more air defence systems to counter Russia's increased bombardment. It also wants help in setting up mobile heating systems to replace damaged power lines.
An aide to Mr Zelenskyy said engineers on the power grid were sometimes working under fire as they tried to restore the damaged infrastructure.
Ukrenergo said Russia was hitting civilian infrastructure because it “cannot compete on the battlefield” with Ukraine's forces, echoing a similar assessment by British intelligence.
Kyiv hit by kamikaze drones — in pictures
The US, Britain and France called for the UN Security Council to hear claims that Russia illegally bought unmanned aerial vehicles from Iran that are now being used in Ukraine.
“There is ample evidence that Russia is using Iranian-made UAVs in cruel and deliberate attacks against the people of Ukraine,” said Nate Evans, a spokesman for the US delegation to the UN.
“By procuring these weapons in violation of UN Security Council resolutions, Russia continues to flout international law in its pursuit of a senseless and brutal war against Ukraine.”
Russia said it was firing with “high-precision long-range air and sea-based armament” at Ukrainian energy plants and military command posts.
The Russian military said it had foiled a Ukrainian attempt to retake the Zaporizhzhia nuclear power plant, where tit-for-tat claims of shelling have led to fears of a nuclear disaster.
