Rescuers are searching through the rubble of a shopping centre looking for more victims of a Russian missile strike that killed at least 18 and wounded scores more in what Ukraine's president called "one of the most daring terrorist attacks in European history".

President Volodymyr Zelensky said many of the more than 1,000 afternoon shoppers and workers inside the building in the city of Kremenchuk managed to escape.

Giant plumes of black smoke, dust and orange flames billowed from the wreckage as emergency crews combed through broken metal and concrete for victims.

Drones whirred above, clouds of dark smoke still emanating from the ruins several hours after the fire was extinguished.

Casualty figures rose as rescuers sifted through the rubble. The regional governor, Dmytro Lunin, said at least 18 people were killed and emergency services reported more than 60 were wounded.

"We are working to dismantle the construction so that it is possible to get machinery in there since the metal elements are very heavy and big, and disassembling them by hand is impossible," said Volodymyr Hychkan, an emergency services official.

At Ukraine's request, the UN Security Council scheduled an emergency meeting in New York on Tuesday to discuss the attack.

In the first Russian government comment on the missile strike, the country's first deputy permanent representative to the United Nations, Dmitry Polyansky, alleged multiple inconsistencies that he did not specify, claiming on Twitter that the incident was a provocation by Ukraine.

Russia has repeatedly denied it targets civilian infrastructure, even though Russian attacks have hit other shopping centres, theatres, hospitals, schools and apartment buildings in the war.

The missile strike occurred as western leaders pledged continued support for Ukraine and the world's major economies prepared new sanctions against Russia, including a price cap on oil and higher tariffs on goods.

Meanwhile, the US appeared ready to respond to Mr Zelensky's call for more air defence systems, and Nato planned to increase the size of its rapid-reaction forces nearly eightfold - to 300,000 troops.

Mr Zelensky said the shopping centre presented "no threat to the Russian army" and had "no strategic value". He accused Russia of sabotaging "people's attempts to live a normal life, which make the occupiers so angry".

In his nightly address, he said it appeared Russian forces had intentionally targeted the shopping centre and added: "Today's Russian strike at a shopping mall in Kremenchuk is one of the most daring terrorist attacks in European history."

He said Russia "has become the largest terrorist organisation in the world".

Russia has increasingly used long-range bombers in the war. Ukrainian officials said Russian Tu-22M3 long-range bombers flying over Russia's western Kursk region fired the missiles, one of which hit the shopping centre and another that struck a sports arena in Kremenchuk.

The Russian strike echoed earlier attacks that caused large numbers of civilian casualties - such as one in March on a Mariupol theatre where many civilians had holed up, killing an estimated 600, and another in April on a train station in eastern Kramatorsk that killed at least 59 people.

"Russia continues to take out its impotence on ordinary civilians. It is useless to hope for decency and humanity on its part," Mr Zelensky said.

The United Nations called the strike "deplorable", stressing that civilian infrastructure "should never ever be targeted", UN spokesman Stephane Dujarric said.

G7 leaders condemned the attack in a statement late Monday, saying "indiscriminate attacks on innocent civilians constitute a war crime. Russian President Putin and those responsible will be held to account".

The attack coincided with Russia's all-out assault on the last Ukrainian stronghold in eastern Ukraine's Luhansk province, "pouring fire" on the city of Lysychansk from the ground and air, according to the local governor.

At least eight people were killed and more than 20 wounded in Lysychansk when Russian rockets hit an area where a crowd gathered to obtain water from a tank, said Luhansk governor Serhiy Haidai.

The barrage was part of Russian forces' intensified offensive aimed at taking the eastern Donbas region from Ukraine. Over the weekend, the Russian military and their local separatist allies forced Ukrainian government troops out of Lysychansk's neighbouring city of Sievierodonetsk.

To the west of Lysychansk on Monday, the mayor of the city of Sloviansk - potentially the next major battleground - said Russian forces fired cluster munitions, including one that hit a residential neighbourhood. Authorities said the number of victims had yet to be confirmed.

The Russian forces also pummelled other Ukrainian cities, killing at least five people and wounding 15 others in Kharkiv, Ukraine's second-largest city, and striking the key southern Black Sea port of Odesa where a missile attack destroyed residential buildings and wounded six people, including a child, according to Ukrainian authorities.