Russian missiles have slammed into the heart of the central Ukrainian city of Vinnytsia, killing at least 23 people, including three children, and wounding dozens.

The Ukrainian Prosecutor-General's office said residential buildings and administrative and office premises had suffered "significant damage and destruction" in the attack.

Kalibr missiles had been fired from a submarine in the Black Sea, Ukraine's military said.

Ukraine's state emergency service said on its Facebook page that 23 people, including three children had been killed, with 66 people admitted to hospital and 39 still missing.

The attack by three missiles also destroyed a medical centre, police said.

Video footage showed thick black smoke billowing out of a tall building and sirens blaring as emergency workers rushed to the scene.

Photographs posted online by the State Emergency Service showed grey smoke later rising from the twisted remains of burnt-out cars and smouldering rubble.

One showed an abandoned, overturned pram lying on the street.

Ukrainian President Volodymyr Zelenskyy said the Russian assault had hit two community facilities and a medical centre, as well as houses and vehicles.

"What is this, if not an open act of terrorism?" Mr Zelenskyy said.

The Russian defence ministry did not immediately comment on the reports from Vinnytsia. Russia, which invaded Ukraine on February 24, has denied deliberately targeting civilians.

Throughout Putin's war against Ukraine, his primary objective has not shifted. What has evolved since February 24 has been the ways and means he has used to achieve it.  

Vinnytsia — a city of 370,000 people, lies about 200 kilometres south-west of the Ukrainian capital Kyiv — hosts the command headquarters of the Ukrainian Air Force, according to an official Ukrainian military website, a target that Russia used cruise missiles to try to hit in March, the Ukrainian air force said at the time. 

The missile strike hit the car park of the nine-storey "Yuvelirniy" office block at about 10:50am local time, the State Emergency Service said.

Ukraine's Interior Minister, Denys Monastyrskyi, later said two more missiles had been intercepted en route by air defences.

In a comment on Twitter, Foreign Minister Dmytro Kuleba accused Russia of committing "another war crime".

"We will put Russian war criminals on trial for every drop of Ukrainian blood and tears," he wrote.

Russia denies its forces have committed war crimes in Ukraine. The Kremlin says it is engaged in a "special military operation" to demilitarise Ukraine and root out what it regards as dangerous nationalists.

Kyiv and its Western allies reject that as a false pretext for an unprovoked war of aggression.

Russian forces have also continued artillery and missile attacks in eastern Ukraine, primarily in the Donetsk province after overtaking adjacent Luhansk.

Some too terrified to leave, others defiant in the face of relentless shelling.

The city of Lysychansk, the last major stronghold of Ukrainian resistance in Luhansk, fell to Russian forces at the beginning of the month.

Luhansk and Donetsk together make up Donbas, a mostly Russian-speaking region of steel factories, mines and other industries.

Donetsk Governor Pavlo Kyrylenko urged residents to evacuate as "quickly as possible".

"We are urging civilians to leave the region, where electricity, water and gas are in short supply after the Russian shelling," Mr Kyrylenko said in televised remarks.

"The fighting is intensifying, and people should stop risking their lives and leave the region."

Two people were killed when Ukrainian forces shelled a bus station in the separatist-held city of Donetsk, a separatist leader said on Thursday.

On Thursday, local time, Daniil Bezsonov, a Russian-backed official in the self-proclaimed Donetsk People's Republic said that forces were focusing their fire in eastern Ukraine in order to seize the towns of Siversk and Soledarand before moving forward to attack the cities of Sloviansk and Kramatorsk from the east.

The same day, the Ukrainian military — which reported Russian shelling of Siversk, Soledar and Kramatorsk — said it was holding the line on all fronts and repelling all attempted assaults.

Russian-backed separatist forces late on Thursday claimed control of the settlements of Stryapivka and Nova Kamianka east of Soledar, the LPR militia said on their Telegram channel.

The British Defence Ministry said on Thursday that despite continued shelling in the Donbas region, Russian forces did not make major territorial gains in recent days.

"The ageing vehicles, weapons and Soviet-era tactics used by Russian forces do not lend themselves to quickly regaining or building momentum unless used in overwhelming mass, which Russia is currently unable to bring to bear," the British ministry said.

Both the Russian forces and Ukrainian militaries are seeking to replenish their depleted stocks of unmanned aerial vehicles to pinpoint enemy positions and guide artillery strikes.

Both sides are looking to procure jamming-resistant, advanced drones that could offer a decisive edge in battle.

Ukrainian officials say the demand for such technology is "immense" with crowdfunding efforts underway to raise the necessary cash for purchases.

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