Russia has targeted Ukraine's power supply and infrastructure in a war more than four years old, while Ukraine has stepped up attacks on Russian oil facilities.
The Kremlin warned that it intended "systematic strikes" on targets in Kyiv in response to a drone attack on a dormitory in Ukraine's Russian-held region of Luhansk, which killed 21.
Ukraine denied the attack.
Photographs showed large explosions and plumes of smoke billowing over high-rise buildings in Kyiv, where overnight strikes killed four people and wounded 65, including children, according to the capital's mayor, Vitali Klitschko.
A suspected missile strike on a 24-storey apartment building triggered a collapse, leaving people probably trapped under the rubble, Klitschko said on Tuesday, while a nine-storey apartment block was among other buildings set ablaze by suspected missile debris.
Thousands seeking shelter flooded into the Kyiv subway system early on Tuesday, witnesses said, some carrying pets, belongings and mattresses, as the sound of defence systems repelling Russian attacks filled the air.
More explosions were heard in the capital after dawn, a Reuters witness said.
Ukraine's air force said Russia launched 656 drones and 73 missiles overnight, mainly targeting Kyiv.
In a statement on Telegram, the air force said 40 missiles and 602 drones had been downed or neutralised.
An air force spokesman said the attack included eight Zircon hypersonic missiles, likely the largest number of those missiles used by Russia during the war.
The Zircon has a range of 1000km and travels at nine times the speed of sound, according to Moscow.
Russia's defence ministry said it had carried out a "massive strike" on Ukraine's defence industry facilities using high-precision long-range weapons.
Seven people were killed and 36 injured in a missile and drone attack on the southeastern city of Dnipro and its surroundings, regional governor Oleksandr Hanzha said on the Telegram messaging app.
All the injured were in hospital in moderate condition, he added, posting pictures of destroyed residential buildings, burnt-out vehicles and a damaged children's playground.
One of dead was a rescue worker who had been killed in a "double tap" strike targeting responders, according to emergency services.
Air raid warnings sounded over much of the country early on Tuesday after Ukrainian President Volodymyr Zelenskiy's warnings the previous day of a possible major assault.
In Ukraine's northeastern region of Kharkiv, a child was among the 10 people injured in drone and missile attacks, mayor Ihor Terekhov said on Telegram.
EU and NATO member Poland scrambled military jets on Tuesday to secure its airspace after the Russian strikes on Ukraine, Poland's military said on X.
Russian regions also came under attack.
The Ilsky oil refinery, in the southern Russian region of Krasnodar, caught fire after a drone attack, local authorities said.
In Russia's Belgorod region bordering Ukraine, an 11-year-old boy was injured after a Ukrainian drone hit a home.
Russia downed a total of 148 Ukrainian drones overnight, Russian news agencies said, citing the defence ministry.
The Ukraine war has ground on since Russia launched its full-scale invasion in February 2022.
Efforts to end it have made little progress, with the administration of US President Donald Trump focused on conflicts in the Middle East.
with DPA
