Emergency power outages have been brought in across almost all of Ukraine after a intensive campaign of Russian air strikes on energy infrastructure.
This will be the fourth consecutive winter of blackouts throughout Ukraine since Russia launched its full-scale invasion in February 2022.
The energy ministry said all but two regions were affected. Only the eastern Donetsk region at the forefront of the war is exempt, while the northern Chernihiv region is already facing hourly outages.
As well as targeting the power network, Russia has increasingly targeted Ukraine's railways. Ukraine has meanwhile ramped up attacks on Russian oil refineries, in border regions and beyond.
One oil depot in the Crimean peninsula - which Moscow illegally annexed from Ukraine in 2014 - has been burning for three days following a second Ukrainian drone attack in a week.
The Marine Oil Terminal in Feodosia is the largest in Crimea and an important logistical link for Russian troops operating in Ukraine.
Kyiv's armed forces general staff said on Wednesday that 16 fuel tanks were damaged and that a large-scale blaze was continuing to burn.
The surge in drone attacks on oil refineries and pipelines has also led to fuel shortages and price rises in some parts of Russia - a development that Ukrainian leaders hope will hit Russia's war effort and help bring the Kremlin to the negotiating table.
The strikes have reduced Russian fuel exports to their lowest level since the start of the war, according to figures from the International Energy Agency.
Ukraine's energy ministry said emergency restrictions were being brought in because of the complicated situation. Emergency work was taking place in all regions affected by Russian attack, grid operator Ukrenergo said, and it urged consumers who still had power to use it sparingly.
Temperatures in parts of Ukraine were forecast to fall to 3C overnight into Thursday.
The electricity company in Lviv in western Ukraine said that because the outages were under emergency conditions there was no possibility to warn consumers in advance.
Russia argues its attacks on Ukraine's energy infrastructure are aimed at its military, but millions of civilians have already been affected by outages in recent weeks. On one night alone last week, on 9-10 October, a combined missile and drone attack caused power cuts in nine regions, from Kharkiv and Sumy in the north to Odesa in the south.
Ukrainian President Volodymyr Zelensky has accused Moscow of aiming to create chaos and apply psychological pressure on the population through strikes on energy facilities and railways.
Kyiv has long been pushing to be given more weapons that could allow it to strike deeper into Russia, and Zelensky this week vowed that long-range weapons would be used only on military targets, not civilians.