Russia attacked Ukraine's capital Kyiv early on Saturday with drones and missiles, triggering fires, strewing debris in districts throughout the city and injuring at least eight people, the city's mayor said.

Reuters witnesses saw and heard successive waves of drones flying over Kyiv, and a series of explosions jolted the city.

Kyiv Mayor Vitali Klitschko said two residents had required hospital treatment and that air defence units were in action.

Pictures posted online showed smoke billowing from the top of one block of apartments and flames leaping from part of another as emergency crews trained water on it. An orange-red glow lit up the city as plumes of smoke wafted across the horizon.

Klitschko said fragments from one drone struck the top floor of an apartment building in the Solomyanskyi district on the west bank of the Dnipro River, which bisects the city. One apartment building was on fire in the area, as was one non-residential building.

Timur Tkachenko, head of Kyiv's military administration, said a fire had also broken out on two floors of an apartment building in the Dniprovskyi district on the opposite bank.

Officials also reported a fire in Obolon in the city's northern suburbs and fallen debris on a shopping centre in the same area. They said drone fragments hit the ground in a number of other widely separated neighbourhoods.

An air alert remained in effect more than two hours after it was first declared.

The overnight strikes followed several days of Ukrainian drone attacks — some 800 attacks — on targets inside Russia, including capital Moscow.

Russian Foreign Minister Sergei Lavrov had vowed on Friday to respond to those attacks.

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Drone use increasing as war rages on

Russia and Ukraine have increasingly turned to drones to strike targets along the front lines and beyond.

The two countries have been locked in a state of all-out war ever since Russia launched a full-scale invasion of its neighbour in February 2022.

Ukrainian officials have repeatedly signalled that drones and related technologies remain critical to its fight against the continuing Russian invasion.

This past week, Valerii Zaluzhnyi, the Ukrainian ambassador to the United Kingdom, said Russia had been waging a war of attrition for more than a year and, given Ukraine's smaller forces and difficult economic circumstances, Kyiv's only hope was to rely on advanced technology.

"We can speak only about a high-tech war of survival, using a minimum of human resources, a minimum of economic means to achieve maximum benefit," Zaluzhnyi, who previously served as Ukraine's army chief, said during a speech at a forum in Kyiv on Thursday.