Ukrainian authorities issued new air raid alerts across the country on Tuesday as Russian bombers took to the skies, a day after Moscow carried out a "massive" attack on Ukraine's power grid.

Russia fired hundreds of drones and missiles at Ukraine on Monday, killing at least four people and battering the country's already weakened energy grid, officials said.

The Russian attack triggered widespread blackouts and came after Kyiv claimed new advances in its incursion in Russia's Kursk region.

Ukraine's air force confirmed early Tuesday the "takeoff of several Tu-95MS from the Engels airfield" in western Russia, prompting air raid alerts across the country.

At least four more people were killed in overnight Russian attacks, according to local officials, two in southeastern Zaporizhzhia and two in the central city of Kryvyi Rig after a missile struck a hotel.

Two more were missing in Kryvyi Rig, "likely under the rubble", regional governor Sergiy Lysak said in a post on Telegram.

On Monday, President Volodymyr Zelensky said Moscow launched at least 127 missiles and 109 drones in "one of the biggest Russian attacks".

Of those, 102 missiles and 99 drones were shot down, according to Ukrainian Air Force Commander Mykola Oleshchuk, who described it as Russia's "most massive" attack.

The United States and Britain both condemned the assault, with US President Joe Biden calling it "outrageous" and British Foreign Secretary David Lammy branding it "cowardly".

Germany's foreign ministry said that "once again, Putin's Russia is saturating Ukraine's lifelines with missiles".

'Very scary' 

State-owned electricity supplier Ukrenergo announced emergency power cuts to stabilise its system following the barrage, while train schedules were disrupted.

Residents in the capital Kyiv rushed to take shelter in metro stations early Monday, as AFP reporters heard the booms of what appeared to be air defences.

"We are always worried. We have been under stress for almost three years now," said Yulia Voloshyna, a 34-year-old lawyer taking refuge in the Kyiv metro.

"It was very scary, to be honest. You don't know what to expect," she said.

Since invading in February 2022, Russia has launched repeated large-scale drone and missile attacks on Ukraine, including punishing strikes on energy facilities.

The Russian defence ministry confirmed it hit energy facilities in a statement, claiming that they were being used to aid Ukraine's "military-production complex".

The attacks early on Monday killed at least four people and wounded over 20 people across the country, officials said.

Two others were killed in later strikes during the day, according to authorities.