"During the rescue operation, 15 bodies were found at the scene and five people were pulled out of the rubble" alive in the town of Chasiv Yar, the local branch of the Ukrainian emergency service said on Facebook.

"At least 30 others are under the rubble" of the four-storey after it was hit by a Russian Uragan missile, Donetsk regional governor Pavlo Kyrylenko said earlier on Telegram.

The building was partially destroyed in the strike, AFP correspondents saw at the scene where rescuers were sifting through the rubble with a mechanical digger.

Rescuers had so far been able to establish contact with three people under the rubble, emergency services said.

Having fought long battles to capture the last areas of the neighbouring region of Lugansk, Russian troops are now turning their focus to Donetsk as they look to take control of the whole Donbas region.

"I was in the bedroom, I came out and everything started shaking, collapsing," a Chasiv Yar resident who did not wish to give her name told AFP.

"What saved me was the force of the explosion pushing me into the bathroom, covered in blood. I barely got out," she said.

'Absolutely Deliberately' 

The Donetsk region was under persistent shelling, while Russian ground attacks were all but paused, the Ukrainian army general staff said Sunday.

On Saturday, three people were killed and a further 23 injured by shelling in Donetsk, governor Kyrylenko said.

Strikes were also reported in Kharkiv, Ukraine's second city in the northeast, where a "teaching establishment" and a house were hit, injuring one, according to regional governor Oleg Sinegubov.

Ukrainian President Volodymyr Zelensky condemned the widespread Russian bombardments in an address Saturday night.

"In just one day, Russia hit Mykolaiv, Kharkiv, Kryvyi Rig, the communities of the Zaporizhzhia region," Zelensky said.

Russian strikes "absolutely deliberately" and "purposefully" targeted the residential sector, hitting "ordinary houses, civilian objects, people", he said.

"Such terrorist actions can really only be stopped with weapons, modern and powerful," Zelensky added, thanking the United States for its latest military aid package.

In a boost to Kyiv, Washington has signed off on a $400 million package, including four additional High Mobility Artillery Rocket Systems to add to eight already in place and high-precision artillery ammunition not previously sent to Ukraine.

"It's a further evolution in our support for Ukraine in this battle in the Donbas," a senior defence official was quoted by the US Department of Defense as saying.