President Volodymyr Zelenskiy said Russia had launched nearly 300 drones, 18 ballistic missiles and seven cruise missiles during overnight attacks on eight Ukrainian regions.
The main targets early on Tuesday were energy-generation facilities and substations, Zelenskiy said in a post on the Telegram app.
"Every such strike against life is a reminder that support for Ukraine cannot be stopped. Missiles for air defence systems are needed every day, and especially during winter."
Ukrainian air defence units shot down 247 drones and seven missiles, the air force said.
It also said on the Telegram app that missiles and drones caused damage at 24 sites.
Emergency power cuts were introduced in the capital Kyiv and also in the Chernihiv, Odesa, Kharkiv, Dnipropetrovsk, Zaporizhzhia and Donetsk regions, the Energy Ministry said.
DTEK, the country's largest private energy company, said the Russian attack heavily damaged equipment at one of its thermal power plants.
Russia has relentlessly targeted Ukraine's energy system throughout the conflict, claiming attacks on civil infrastructure are justified to impair Ukraine's war effort.
Kyiv says Moscow's aim is to inflict suffering to break the national will.
Ukrainian officials say the war's fourth winter is shaping up to be the coldest and darkest yet, with Russian strikes intensified, years of cumulative damage taking a toll and the weather dangerously cold even for Ukraine's climate.
Temperatures are hovering at about -13C in Kyiv where residents have endured days with interrupted electricity and heating supplies after the last big Russian strike last week.
Weeks before the fourth anniversary of Russia's full-scale invasion, diplomatic efforts to end the war have brought no tangible results and Russian troops are slowly advancing in Ukraine's eastern Donetsk region in costly battles.
Russia's defence ministry said that its troops carried out a massive strike targeting military-industrial facilities in Ukraine.
In the city of Kharkiv, 30km from the border with Russia and a frequent target, four people were killed during the attacks when a postal terminal was hit by several missiles and drones, said regional governor Oleh Syniehubov.
"We faced a mass Shahed and missile attack," said Syniehubov, referring to Iranian-designed drones.
"More than 30 people were wounded. Four people were killed on site."
In the southern port city of Odesa, at least five people were injured as a result of the overnight Russian attack, the emergency service said. It reported fires at an unused new building, a fitness centre and a vocational school.
Two people were injured as a result of a Russian attack on the industrial city of Kryvyi Rih in central Ukraine which damaged civilian infrastructure, homes and gas pipelines, the region's governor said.
