Already displaced from the frontline region of Kharkiv that has been partially occupied since Russia invaded Ukraine in February, Alia Skrypka, 35, believed that Kremenchuk, more than 170 km from the nearest fighting, was safe.

But after a missile strike on a shopping mall killed at least 18 people in the central Ukrainian city on Monday, she is now considering whether she should move her two girls, Milla, 7 and Myroslava, 4, elsewhere - and perhaps even abroad.

"After this, I'm not sure we are safe," she said, after helping her elder daughter to place flowers at an unofficial memorial just metres from the burned husk of the mall.

The industrial city, home to Ukraine's largest oil refinery, had already been hit by several strikes, but residents said earlier attacks had not hit civilian areas.

Russia said its strike was aimed at an ammunition store. The mall is next to a factory that Ukraine says was disused and could not be described as a military target.

Russia denies intentionally targeting civilians in its "special military operation" in Ukraine which has destroyed cities, killed thousands of people and driven millions from their homes.

At least one rocket crashed into the busy shopping centre on Monday afternoon, killing at least 18 and injuring dozens, according to officials. Another 41 people were unaccounted for, Poltava regional governor Dmytro Lunin said on Tuesday.

Many shoppers and staff had ignored an air-raid siren that began about 10 minutes earlier. Survivors described a maelstrom of shrapnel and debris after the strike.

Residents of Kremenchuk visited the makeshift memorial to leave flowers, soft toys and candles throughout the day on Tuesday, even as machinery worked in the background to clear the debris.

Mother of three Ania Miakushka, 44, was in tears as she laid flowers, clutching her 5-year-old son's hand and touching at a graze on his shoulder. Her own hands are also cut up from when the windows of her home were blown out by the missile blast.

The family had been gathered around the dinner table after a funeral for a relative when the blast hit, she said.

"My elder son says we should leave, but I don't have anywhere to go," she said.

But as elsewhere in Ukraine, life goes on and many ignore the frequent air-raid sirens, deciding that taking shelter each time is too much of a disruption.

During an air-raid alert in Kremenchuk on Tuesday, Ukraine's Interior Minister Denys Monastyrskyi, one arm in a bandage after giving blood for those injured in the strike, sheltered in the basement of a hotel.

He said Monday's missile strike was a reminder to Ukrainians to heed air-raid sirens.

In the same basement, Tatiana, who only agreed to give her first name, said she did not take shelter on Monday, and was in the middle of a salon appointment when the siren sounded on Tuesday.

"I was having my hair colored, but I came straight down," she said, her hair still wrapped in a towel.