Russian air attacks on major Ukrainian cities such as Kyiv, Dnipro and Kharkiv killed at least nine and wounded more than 60, authorities said, following days of warnings that Moscow was planning a major assault.
Russia has targeted Ukraine's power supply and infrastructure while Ukraine has stepped up attacks this year on Russian oil facilities in a war now more than four years old, sometimes causing casualties, but both deny targeting civilians.
Five people were killed and 25 injured in a Russian missile and drone attack on the southeastern city of Dnipro, regional governor Oleksandr Hanzha said on messaging app Telegram.
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.
At least four were killed and 51 injured, including children, across the capital of Kyiv, Mayor Vitali Klitschko said.
A suspected missile strike on a 24-storey apartment building triggered a collapse, leaving people probably trapped under the rubble, Mr Klitschko said.
A nine-storey apartment block was among other buildings set ablaze by suspected missile debris, he added.
"In the Obolon district, cars are burning after being struck by falling missile debris," Mr Klitschko said.
"There are also fires at two locations in open areas, including one near a kindergarten."
Thousands of residents flooded into the Kyiv subway system seeking shelter, witnesses said, some carrying belongings and mattresses, as the sound of defence systems repelling Russian attacks filled the air.
Warnings of a major attack
Air raid warnings sounded over much of the country early after Ukrainian President Volodymyr Zelensky reiterated warnings the previous day of a possible major assault.
"Intelligence warnings regarding Russian strikes remain in effect. A massive strike is possible. They have prepared one," Mr Zelensky said in his nightly video address.
"Our defenders are ready 24/7 to the fullest extent possible with the supplies currently available."
Russia warned last week that it intended "systematic strikes" on targets in Kyiv linked to the Ukrainian military as well as decision-making centres and urged foreigners to leave.
It said the action was in response to a drone strike last month on a dormitory in Ukraine's Russian-held region of Luhansk, which killed 21. Ukraine denied the attack.
In Ukraine's northeastern region of Kharkiv, a child was among 10 injured in drone and missile attacks, Mayor Ihor Terekhov said on Telegram.
Russia's Ilsky oil refinery, in the southern region of Krasnodar, caught fire after a drone attack, local authorities said on Telegram.
Air defence systems were also repelling drone attacks over Sevastopol, a Russian naval fleet base, in Russia-occupied Crimea, authorities there said.
Reuters could not independently verify all the reports.
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.
