Russian forces launched at least 60 missiles across Ukraine on Friday, officials said, reporting explosions in at least four cities, including Kyiv.
At least two people were killed by a strike on a residential building in central Ukraine, where a hunt was on for survivors.
Electricity and water services were interrupted in the capital and Ukraine's second-largest city, Kharkiv. Thousands of people sought shelter in subway stations deep underground during the bombardment.
The Kyiv city administration said Ukraine's capital had withstood "one of the biggest rocket attacks" launched by Russian forces since they invaded Ukraine nearly 10 months ago. The administration said Ukrainian air defense forces shot down 37 of "about 40" that entered the city's airspace. One person was injured, it said.
Thudding blasts and gunfire from air-defense systems echoed across the country as authorities on social media reported explosions and missile strikes in the city and southern Kryvyi Rih, southeastern Zaporizhzhia, and northeastern Kharkiv. Air raid alarms sounded across the country, warning of a new barrage of the Russian strikes that have occurred intermittently since mid-October.
Ukrainian Air Force spokesman Yurii Inhat told Ukrainian TV that more than 60 missiles had been fired, but it wasn't immediately clear how many missiles the Ukrainian army managed to intercept.
Ihnat said Russian forces had fired cruise missiles from positions in the Black Sea, and used bomber aircraft as part of an effort to "massively distract the attention of the anti-aircraft defense, keeping it in tension."
At the site of one attempted strike in Kyiv, military commanders told The Associated Press that the city's territorial defense mobile group had unexpectedly, "almost unbelievably,” shot down a cruise missile with a machine gun.
"Almost impossible to hit a missile with a machine gun, but it was done," said a commander who goes by the call sign "Hera."
Another commander, a military post chief named "Yevhen," said the machine gunner who intercepted the missile. "reacted quickly" and fired, and green sparks flew from the rocket as it began to spin and tumble to the ground.
A day earlier, Russia's Foreign Ministry warned that if the United States delivers sophisticated Patriot air defense systems to Ukraine, such systems and any crews that accompany them would also be a legitimate target for the Russian military. Washington rejected that threat.
Analysts have said Russian strikes targeting energy infrastructure have been part of a new strategy to try to freeze Ukrainians into submission after recent battlefield losses by Russian forces. Officials and experts say that has only strengthened the resolve of Ukrainians to face up to Russia's invasion, while Moscow tries to buy time for a possible offensive in coming months after the current battlefield stalemate.
In Kryvyi Rih in central Ukraine, President Volodymyr Zelensky's hometown, a missile slammed into a four-story residential building and left a gaping hole in its upper floors, with rubble spilling onto the ground. Two people were killed and at least eight others were injured, including three children, regional Gov. Valentyn Reznichenko said.
Rescue teams were combining through the debris in a hunt for survivors or other victims.
The southeastern city of Zaporizhzhia was struck by about 15 Russian missiles, regional Gov. Oleksandr Starukh said. He did not specify the exact location of the strikes, but said infrastructure had been damaged.
Kharkiv Mayor Ihor Terekhov said on Telegram that the city was without electricity. Kharkiv regional governor Oleh Syniehubov reported three strikes on the city's critical infrastructure. Kyiv Mayor Vitali Klitschko reported explosions in at least four districts and urged residents to go to shelters.
"The attack on the capital continues," he wrote on the social media app. Subway services in the capital were suspended, he said, as city residents flocked inside its tunnels to seek shelter.
Ukrzaliznytsia, the national railway operator, said power was out in a number of stations in the eastern and central Kharkiv, Kirovohrad, Donetsk and Dnipropetrovsk regions, due to damage to the energy infrastructure. But trains continued to run by switching from electric power to steam-engine power, which had been readied as a backup.
In neighboring Moldova, the state-owned energy company Moldelectrica reported disruptions to its electricity network as a result of Russia's strikes on Ukraine, and warned of a "high risk" of power outages.
Moldova, whose Soviet-era systems remain interconnected with Ukraine's, has already suffered two massive blackouts in recent months as Russia attacked Ukraine's energy grid.
The previous such round of massive Russian air strikes across the country took place on Dec. 5. Ukrainian authorities have reported some successes in intercepting and downing incoming missiles, rockets and armed drones.