Ukraine's Zaporizhzhia nuclear power plant has been left without electricity supply following a Russian strike and is currently running on diesel generators, the country's nuclear energy operator said on Thursday.

"The last line of communication between the occupied Zaporizhzhia NPP and the Ukrainian power system was cut off as a result of rocket attacks," Energoatom said in a statement.

Meanwhile, pre-dawn Russian strikes targeted energy infrastructure across Ukraine on Thursday, prompting massive power outages including at Europe's largest nuclear power plant.

For months Russia has been pummelling key facilities in Ukraine with missiles and drones -- disrupting water, heating and electricity supplies for millions of people.

Kyiv mayor Vitali Klitschko said 15 percent of households were without power and 40 percent without heating following explosions in two areas of the Ukrainian capital.

"Two people were injured," he said.

Ukraine's nuclear energy operator said the strikes had also cut off the electricity supply to the Zaporizhzhia nuclear power plant, which is controlled by Russian forces and is Europe's largest.

For the sixth time since it was taken over, the facility is now operating on diesel generators which have an autonomy of 10 days.

"The countdown has begun. If it is impossible to renew the external power supply of the station during this time, an accident with radiation consequences for the whole world may occur," Energoatom said.

There were also strikes reported on energy plants in several other parts of Ukraine, including Kharkiv in the northeast and the region of Odesa in the southwest.

In the Kharkiv region, located on the border with Russia, governor Oleg Synegubov said there had been 15 strikes.

"The occupiers once again targeted critical infrastructure facilities," he said on social media.

Synegubov added that information on victims and the scale of the damage was being "clarified".

In the region's main city of Kharkiv, mayor Igor Terekhov said "energy infrastructure" had been targeted and there were "problems" with electricity in some parts of the city.

In Odesa region, governor Maksym Marchenko said "missiles hit the energy infrastructure of the region as well as damaged residential buildings" following a "massive missile strike".

"Fortunately, there were no casualties," he said, adding that "power supply restrictions" were in place.

- Bakhmut may fall -

The wave of strikes comes after Russia reported making gains in the battle for the industrial city of Bakhmut, which has been the focus of months of fierce combat.

Russia's Wagner mercenary group, which has spearheaded the attack on Bakhmut, claimed on Wednesday to have captured the eastern part of the city.

"What we see is that Russia is throwing more troops, more forces and what Russia lacks in quality they try to make up in quantity," NATO Secretary General Jens Stoltenberg told reporters in Stockholm on the sidelines of an EU defence ministers meeting on Wednesday.

"We cannot rule out that Bakhmut may eventually fall in the coming days," the head of the US-led military alliance said, adding that "this does not necessarily reflect any turning point of the war".

Ukrainian officials have warned that the fall of Bakhmut could lead to further Russian advances in eastern Ukraine.

Ukraine's Deputy Defence Minister Ganna Maliar said on Wednesday that the resistance in Bakhmut should be considered a "victory".

"This is victory -- the fact that our soldiers have been destroying the most powerful and professional 'Wagner' units there for several months in a row.

"The enemy has superior forces in terms of manpower and weapons, but in these conditions, our fighters bravely confront the enemy almost on an equal basis," she said.

- More ammunition needed -

Ukrainian President Volodymyr Zelensky also on Wednesday hosted UN chief Antonio Guterres in Kyiv, who was on his third visit to Ukraine since Russia's invasion.

Guterres stressed the need to extend a deal that has allowed Ukraine to export its grain but is due to expire.

"I want to underscore the critical importance of the rollover of the Black Sea Grain Initiative on 18 March," Guterres said.

At their meeting in Stockholm, the EU defence ministers also discussed a plan to rush one billion euros' worth of ammunition to Ukraine as pressure mounts on Kyiv's allies to bolster supplies to the war effort.

Ukraine's Western backers warn that Kyiv is facing a critical shortage of 155-millimetre howitzer shells as it fires thousands each day in its fight against the grinding Russian offensive.

"The current rate of consumption compared to the current rate of production of ammunition is not sustainable, and therefore we need to ramp up production," Stoltenberg said.