"The occupiers made at least 10 strikes on the critical infrastructure of the city of Kharkiv and the region," Oleg Synegubov said in a post on Telegram, adding no casualties had been reported.

The Russian army used "missiles" to strike Ukraine's second most populous city, Kharkiv mayor Igor Terekhov said on Telegram.

The Ukrainian air force said earlier that around nine Russian Tu-95MS strategic bombers were in the air and were suspected of preparing to launch missiles towards Ukraine.

"Judging by where the Russian aggressor is aiming, problems with energy supply are possible in Kharkiv," Terekhov said in an earlier Telegram post.

The regional governor said on Thursday morning that action was being taken to deal with power cuts.

In the southern region of Zaporizhzhia, governor Ivan Fedorov reported "explosions" early Thursday.

Moscow has heavily targeted Ukraine's energy facilities over recent months, launching some of its biggest aerial strikes of the two-year war.

Missiles hit two regions in Ukraine on Wednesday killing seven people, local authorities said.