As the Russian assault on Kyiv steps up, some of the city's most vulnerable residents can't leave.

For the Ukrainian capital's largest children's hospital, shutting down is not an option, even with the sound of heavy fighting and shelling outside. Children who are too sick to be transferred have been moved to the basement, in case bombardment starts again. There are about 10 patients being treated in the underground hallway, where exhausted staff hover nervously, CNN writes.

One of the patients is 3-month old Milena, who has a brain tumour. Her mother, Sonia, told CNN she had been sleeping on the floor next to Milena for the past seven nights as the bombing gets closer.

“We must stay underground and we don't know how long for,” she said. “I'm alone here at the hospital and my husband is at home with my other kid.”

She said she has become so stressed that she can't lactate, and is now using a formula to feed her daughter.

Resources are stretched tight as hospitals deal with trauma injuries — so some parents have stepped in to help care for other children in the basement. Non-essential procedures are now on hold. When CNN visited the hospital, one 11-year-old boy needs to have his sutures removed — but the risk of infection is too high.

With no clear end in sight, for many families here the only glimmer of hope is evacuation. On Thursday, Ukrainian and Russian delegations met in Belarus for another round of talks, where they agreed to provide humanitarian corridors for civilians and a possible temporary ceasefire in areas where evacuation is happening.