Russia has launched more than 50 missiles targeting critical infrastructure across Ukraine, including the capital Kyiv, causing power and water outages, Ukraine says.
One Kyiv resident told the BBC his district was without electricity after the massive attack on Monday morning.
In the north-eastern city of Kharkiv, energy facilities were hit.
The strikes come after Russia blamed Ukraine for a drone attack on its Black Sea Fleet in the annexed Crimea.
Kyiv Mayor Vitlaiy Klitschko said 80% of city residents were left without water supply after an energy facility near the capital was damaged. He also said that engineers were urgently deployed to restore electricity supply to about 350,000 apartments in the megapolis.
The city authorities said that "no hits wee recorded" in Kyiv itself due to "the effective work of the air defence forces".
On Monday morning, missile strikes were also reported in the central Vinnytsia region, as well as Dnipropetrovsk and Zaporizhzhia in the south-east, and Lviv in western Ukraine.
A facility at the Dnipro hydroelectric power plant in the Zaporizhzhia region was also reportedly hit.
It was not immediately known if there were any casualties.
Residents in the regions under attack were urged to remain in shelters, amid fears more strikes could follow. They were also warned that "emergency power outages" were being rolled out across the country.
Ukraine's Air Force spokesman Yuriy Ihnat told Ukrainian TV that Russia had used its strategic bombers to carry out its "massive" strikes.
Ukraine's military later said that 44 out of more than 50 X-101 and X-555 cruise missiles launched from Russia's Rostov region and also the Caspian Sea had been shot down.
Ukrainian Foreign Minister Dmytro Kuleba said that "instead of fighting on the battlefield, Russia fights civilians".
Russia has carried out several waves of deadly missile and drone attacks in recent weeks, reportedly destroying almost a third of Ukraine's power stations and other energy-generating facilities ahead of the cold winter period.
Ukraine and its Western allies have repeatedly said that targeting civilian infrastructure amounted to war crimes.
Russia has so far made no public comments on the reported latest strikes.
On Saturday, one Russian warship was damaged in the port city of Sevastopol in a drone attack, the Russian defence ministry said. It also accused British specialists of having trained the Ukrainian soldiers who then carried out the strikes in Crimea - Ukraine's southern peninsula, annexed by Russia in 2014.
Moscow provided no evidence to back its claims.
Ukraine has not commented on the issue, while the UK defence ministry said Russia was "peddling false claims on an epic scale".