Russian missile strikes on energy infrastructure in regions across Ukraine have killed at least one person and injured at least 20 more in the early hours of Christmas Day, according to local authorities.

In the north-eastern city of Kharkiv, a "massive missile attack" hit about 7am, local time, and injured at least six people, the city's mayor said.

Kharkiv Mayor Igor Terekhov said in a statement on Telegram that he believed ballistic missiles were used in the attack.

"Kharkiv is under a massive missile attack," Cr Terekhov said.

"A series of explosions were heard in the city, and there are still ballistic missiles heading towards the city."

Ukraine's air defences downed 59 of 78 Russian missiles and 54 of 102 drones launched overnight and on Wednesday morning, the Ukrainian military said.

Kharkiv's regional governor, Oleh Syniehubov, said on Telegram that there were "damages to civilian non-residential infrastructure" in the strikes.

He said he had counted seven Russian strikes and said casualties were still being assessed.

Ukrainian President Volodymyr Zelenskyy said Russian President Volodimir Putin "deliberately chose" Christmas Day for the attack.

"What could be more inhuman? More than 70 missiles, including ballistic missiles, and more than a hundred attack drones," Mr Zelenskyy said on Telegram.

He said there were hits and blackouts in several regions because of the strike.

The Ukrainian Energy Minister German Galushchenko wrote on Facebook on Wednesday that energy operators have limited supply to minimise the impacts of the strikes.

Romania was unable to verify claims by Kyiv that a Russian missile would have passed through Romanian airspace

Border police in neighbouring Moldova said they had recovered a Russian missile but it had not passed through its airspace.

Energy grid attack extended to Dnipro

The Russian Defence Ministry confirmed on Wednesday that it had targeted critical energy facilities in Ukraine in a "massive strike", but claimed these supported Kyiv's military-industrial complex.

It said in the same statement that Russian forces had also taken control of the settlement of Vidrodzhennia in eastern Ukraine.

In the Dnipro region, more than 200 kilometres south of Kharkiv, Russian forces appeared to be "trying to destroy the region's power system", according to a statement on Telegram by Governor Serhiy Lysak.

"Since the morning, the Russian army has been massively attacking the Dnipro region," Mr Lysak said.

A search and rescue operation after the strikes on Christmas Eve found a 43-year-old man had been killed and 17 others wounded, the governor said.

Ukraine's largest private energy company, DTEK, said in a statement after 8am that the strikes had hit its power plants, severely damaging energy equipment.

"This year, it is the 13th massive attack on the Ukrainian energy sector and the 10th massive attack on the company's energy facilities," DTEK said in a statement on Telegram.

Earlier on Wednesday, the Ukrainian military launched a countrywide air alert in response to Russian cruise missile launches.

Local authorities and the air force reported missile sightings in the skies over the eastern, central, southern and western regions.

Air raid sirens rang out in cities across the country, with the Ukrainian military issuing alerts for Russian Kalibr cruise missiles being launched from the Black Sea.

Drone debris causes fatal fire in Russia

Russia's defence ministry said on Wednesday that its forces had shot down 59 Ukrainian drones overnight, while the Ukrainian Air Force reported the launch of Kalibr cruise missiles from the Black Sea, although it was not initially clear where they were headed.

Falling debris from a Ukrainian drone that was shot down caused an explosion and a fatal fire in a shopping centre in the city of Vladikavkaz in Russia's North Ossetia region, the local governor said on Wednesday.

Sergei Menyailo wrote on Telegram that air defence systems had shot down the drone after 8am Moscow time.

One woman was reported to have been killed inside the shopping centre.

Also on Wednesday, the acting governor of Russia's Kursk region said four people had been killed and five injured after Ukrainian shelling in the Kursk town of Lgov.

"A five-storey residential building, two single-storey residential buildings and a single-storey beauty salon were seriously damaged," Alexander Khinshtein wrote on Telegram.

"The blast wave blew out windows in neighbouring private residences and damaged at least 12 cars. A small section of a gas pipeline was also destroyed by the blast."

Pope Francis delivered a Christmas message on Wednesday which called for "the boldness needed to open the door to negotiation" between Russia and Ukraine.

He also called for "gestures of dialogue and encounter, in order to achieve a just and lasting peace".

"May the sound of arms be silenced in war-torn Ukraine!" he said.

AFP/Reuters