Russia unleashed a missile barrage across Ukraine on Wednesday, forcing shutdowns of nuclear power plants and killing civilians in Kyiv as Moscow pursued a campaign to plunge Ukrainian cities into darkness and cold with winter setting in.

All of the capital region, where over three million people live, was deprived of power and running water, Kyiv's governor said, as were many other regions where emergency blackouts were necessary to help conserve energy and carry out repairs.

Ukraine will seek an urgent meeting of the United Nations Security Council, President Volodymyr Zelenskiy said.

"The murder of civilians and the destruction of civilian infrastructure are acts of terror. Ukraine will continue to demand a decisive response from the world to these crimes," he said in a tweet.

Officials across the border in Moldova said electricity was also lost to more than half of their country, the first time a neighbouring state has reported such extensive damage from the war in Ukraine triggered by Russia's invasion nine months ago.

Blackouts forced the shutdown of reactors at Ukraine's Pivdennoukrainsk nuclear power plant in the south and the Rivne and Khmelnitskyi plants in the west, all in government-held territory, the state-run nuclear energy firm Energoatom said.

"Currently, they (power units) work in project mode, without generation into the domestic energy system," Energoatom said.

Ukraine's largest nuclear complex, at Zaporizhzhia near the front lines in the south, is Russian-controlled and was previously switched off because of shelling that both sides blame on each other.