Five "powerful" Russian missiles hit Lviv on Monday, a city in the west of the Ukraine that has so far been spared much of the fighting since Russia invaded its pro-Western neighbour nearly two months ago, the city's mayor said.

A Lviv resident told AFP they could see thick clouds of grey smoke in the sky above some blocks of flats. The city's mayor, Andriy Sadovy, wrote on Telegram that rescue services were at the site. 

The strikes in Lviv come as Russian forces have over recent days been intensifying strikes on the capital Kyiv further east, targeting several facilities that produce military hardware.

"Five powerful missile strikes at once on the civilian infrastructure of the old European city of Lviv," Ukrainian presidential aide Mykhaylo Podolyak wrote on Twitter.

"The Russians continue barbarically attacking Ukrainian cities from the air, cynically declaring to the whole world their 'right' to kill Ukrainians," he added.

Sadovy said there had been no immediate confirmation of any deaths or injuries following the strikes.

Lviv in late March was hit by a series of Russian strikes that targeted a fuel depot and injured five people. On March 18, bombardments hit  an aircraft repair factory near Lviv's airport. No injuries were reported. 

Russian cruise missiles on March 13 targeted a major military base about 40 kilometres (25 miles) north west of Lviv, killing at least 35 people and injuring 134.

Close to the Polish border, Lviv has become a city of refuge for displaced persons and at the start of the war hosted several Western embassies transferred from Kyiv.