"Russia has escalated to massive strikes on energy infrastructure," Prime Minister Sergii Koretskyi said on Telegram on Wednesdasy, adding that energy facilities had come under attack in other regions as well.
"Since summer, there's barely been a day without an attack on our energy infrastructure. But a combined strike of this scale hasn't happened since the end of last heating season."
Ukraine is preparing for another winter assault on power and heating facilities after 2025 entire cities were plunged into darkness and cold for days or weeks.
Koretskyi instructed local authorities to check the readiness of back-up power systems at critical facilities, and finish installing and connecting them as soon as possible.
President Volodymyr Zelenskiy said energy infrastructure in the capital and the surrounding region was the main target of the overnight attack that involved nearly 190 drones and ballistic missiles.
Five people, including a child, had been killed across Ukraine, Zelenskiy said.
Power company DTEK did not detail the damage to energy infrastructure in Kyiv but said workers had restored supply to 8000 households.
Russia acknowledged the massive overnight assault, saying it had hit a data centre in the capital supporting Ukraine's armed forces, various power plants in the Kyiv region, an industrial complex in Odesa region, and port infrastructure in Izmail.
The attacks followed weeks of near-constant barrages of jet drones, which Ukraine struggles to shoot down.
Zelenskiy said Ukraine - which is also short of interceptors to down ballistic missiles - had received new air defence support packages in recent days.
Thanking allies for the deliveries, he called for more protection before the winter.
Ukraine's air force said five missiles and 155 drones had been intercepted in the overnight attack.
On Wednesday morning, Kyiv was shrouded in thick fog from the smoke of attacks.
Citing preliminary information, Klitschko said debris had been found at a Western embassy in the centre of Kyiv.
Among neighbouring nations, a drone crossed into Moldova's airspace and exploded near the eastern village of Hirbovet, while European Union and NATO members Romania and Poland both scrambled military jets, the countries said.
Flights at Polish airports Lublin and Rzeszow were temporarily suspended.
Ukraine has also increased attacks on Russia, hitting refineries and online retailers to undermine Moscow's war effort.
One person was killed in drone attacks in Russia's Bryansk region, which borders Ukraine, while a Ukrainian drone attack on the oil-producing Samara region damaged private houses, regional governors said.
