The whole of Ukraine’s western city of Lviv is without power after widespread strikes were reported across the country.
Ukraine’s neighbour Moldova also reported “massive” blackouts, although it has not been directly hit.
Kyiv city administration said three people had been killed, and the head of the wider Kyiv region said critical infrastructure and homes had been hit.
Russia has recently increased its attacks on Ukrainian energy networks.
More than half of Moldova was without electricity, deputy prime minister Andrei Spinu wrote on Twitter.
“Massive blackout in Moldova after today’s Russian attack on Ukraine’s energy infrastructure,” he said.
Within a few hours power was starting to be restored in the Moldovan capital Chisinau, a Reuters journalist reported.
Earlier, an air-raid alert was issued across Ukraine, followed by reports of explosions in a number of locations.
Lviv mayor, Andriy Sadovy, said children had been taken to shelters with their teachers – and urged parents not to pick them up until the alarm was over.
Shortly before the fresh reports from Kyiv and Lviv, officials said southern Ukraine had come under renewed assault.
The governor of the Mykolaiv region warned of “many rockets” arriving from the south and east.
In the nearby Zaporizhzhia region, a newborn baby was killed when a missile hit a maternity unit, emergency services said.
Russia was blamed for that attack, but is yet to comment on any of Wednesday’s alleged strikes.
Scheduled and unscheduled blackouts have become common in many parts of Ukraine as a result of the recent attacks.
Many areas of Ukraine hit by blackouts on Wednesday were close to neighbouring countries, including Lviv, just 80km (50 miles) from Poland, where a Ukrainian air defence missile killed two people last week.
The towns of Chervonohrad and Yavoriv, also close to the Polish border, suffered power cuts.
Moldova also experienced widespread power cuts as a result of strikes on Ukraine on 15 November, Mr Spinu said. Mobile networks were also badly affected.
Sergiu Tofilat, a local energy policy analyst, told Moldova’s TV8 channel that the country’s energy supplies relied on a power line that passed through Transnistria, a breakaway Russian-controlled territory in Moldova bordering Ukraine, before reaching the capital Chisinau. “When there are bombings in Ukraine, this line is automatically disconnected and we are left without electricity,” he was quoted as saying.
In response to the outages, Moldovan president Maia Sandu said Russia had “left Moldova in the dark”.
“Russia’s war in Ukraine kills people, destroys residential blocks and energy infrastructure with missiles…” she wrote on Facebook, adding: “But the electricity supply can be restored. We will solve the technical problems and we will have light again. All state institutions are working in this direction.”
On Monday Ms Sandu said the war in Ukraine was endangering electricity and gas supplies in Moldova. “We are not certain we can find enough… to heat and light our homes,” she said, warning people to brace for a harsh winter.
Russian attacks have damaged almost half of Ukraine’s energy system, and millions of people are without power as temperatures drop for winter.
In recent days, the head of Ukraine’s biggest private energy firm said people should consider leaving the country to reduce demand on the country’s power network. – bbc.com