Massive Russian drone and missile barrage killed at least 20 people across Ukraine overnight into Wednesday, damaging residential buildings, industrial facilities and infrastructure, officials said.

Emergency services picked through the rubble of the flattened five-story building in Pryluky, in the Chernigiv region, in a frantic search for survivors.

But hopes faded as the toll jumped by early afternoon.

"The death toll ... has risen to 14, including four children," the state emergency services said. "Fifty people were wounded, including seven children."

Fifteen people, including a child, were rescued, they wrote on Telegram.

Ukraine's President Volodymyr Zelenskyy had warned the public Tuesday night that Russia was planning "massive" strikes, particularly against the country's energy infrastructure.

"The Russians wanted to strike painfully and demonstratively," he said Wednesday, calling it "one of the most vile strikes" in the nearly five-year conflict.

Two people were killed when missiles slammed into high-rise buildings in Dnipro and Kremenchuk in central Ukraine, while two others lost their lives in Oleksandriya, he added.

In the capital, Kyiv, strikes killed two people.

Kyiv has come under increased attack in recent weeks as winter approaches, with air raid sirens wailing nearly constantly to warn of incoming Russian strikes.

Residents hunkered down in subway stations overnight, hauling duffel bags, sleeping mats and blankets, after air alerts sounded warning of attacks.

"We grabbed our things and came here, we live right next door," Iryna Rybalchenko, who works in a bank, told AFP, sitting on the platform wrapped in a dark hoodie and surrounded by bags.

"The whole of Kyiv is in a state of fear. We were stuck at work today and everyone – our group chats, our bosses – were messaging us to be careful."

Russia launched at least 50 missiles and 130 drones overnight against several regions including Dnipropetrovsk, Kyiv, Kharkiv, and Poltava, Ukraine's air force said.

Zelenskyy said that although some were shot down, ballistic missiles were "the greatest challenge," and new air defenses were "a vital necessity" to help Ukraine defend itself.

'Tearing Kyiv apart'

The two victims in Kyiv died in a fire in the densely populated Darnytskyi neighborhood as a result of Wednesday's attack, Mayor Vitaly Klitschko said.

He had warned last week the capital should now be on a war footing as the enemy was "tearing Kyiv apart" with strikes on bridges and energy infrastructure.

The renewed attacks had triggered scheduled power cuts Tuesday, which plunged parts of Kyiv into darkness to ease the pressure on the battered grid.

A familiar rumbling sound of the generators, used to get through power cuts, filled the streets again, bringing back memories of the previous winter, when systematic Russian attacks regularly cut power and heating.

In the evening, Zelenskyy warned residents to monitor for air raid sirens, saying in his nightly address that "there is updated intelligence information regarding the preparation by the Russians of a massive strike."

Military monitoring channels also said they expected a large-scale Russian attack, combining cruise and ballistic missiles with fast-moving jet-powered drones.

Zelenskyy said the military was "ready to respond, to the extent that our defense systems allow."

The air force said in the morning that it intercepted five ballistic missiles, as well as 39 cruise missiles and over 100 drones.

Ukraine has been struggling to down the new and fast-moving jet-powered drones, as well as the ballistic missiles that are harder to intercept.

"The children were absolutely terrified. Whenever there's heavy shelling, we try to head underground," Daria Medvedeva, 36, told AFP.

Concern has mounted about rising civilian casualties on both sides, as Ukraine also steps up its long-range attacks on Russian targets that it says are vital to its war effort.

Zelenskyy said Ukraine's "just responses" to Russian strikes saw it hit two oil facilities and a training ground in the Perm, Samara and Astrakhan regions, as well as the Black Sea.