A Russian air strike hit a Ukrainian maternity and children's hospital in the city of Mariupol.
The strike buried patients under rubble and injured women in labour, despite a ceasefire agreement to allow people out of the besieged city.
The children's hospital was destroyed.
A "war crime"
Ukraine president Volodymyr Zelensky, speaking Russian rather than Ukrainian for part of his latest video address, said the attack was a war crime and that people were trapped under the wreckage.
He also posted footage apparently from inside the hospital, which appeared badly damaged.
He asked: "What kind of a country is Russia, that it is afraid of hospitals and maternity wards and destroys them?"
People injured, no deaths
A regional official told Ukrainian media that at least 17 people were injured, including staff and patients.
There were no deaths confirmed, and there were no confirmed injuries amongst children.
Ceasefire but attack still happened
Pavlo Kyrylenko, the head of the Donetsk regional administration said the attack happened during an agreed ceasefire with the Russian side, according to Interfax-Ukraine.
Russia had pledged to halt firing so at least some trapped civilians could escape the city, where hundreds of thousands have been sheltering without water or power for more than a week.
The Mariupol city council said the strike had caused "colossal damage", and published footage showing burned out buildings, destroyed cars and a huge crater outside the hospital.
"We don't understand how it's possible in modern life to bomb a children's hospital. People cannot believe that it's true," Mariupol Deputy Mayor Serhiy Orlov told the BBC.
In response, Kremlin spokesman Dmitry Peskov, told Reuters: "Russian forces do not fire on civilian targets."
Thousands of civilians dead: Ukraine
Mariupol has been surrounded by Russian forces for several days, and repeated attempts at a ceasefire to allow civilians to leave have broken down.
Deputy Mayor Orlov said at least 1,170 civilians had been killed in the city since the Russia invasion on Feb. 24.
Satellite image company Maxar said images from earlier in the day showed extensive damage to homes, apartment buildings, grocery stores and shopping centres in Mariupol.
Russia's defence ministry blamed Ukraine for the failure of the evacuation.
The United States condemned the bombing as "barbaric".
All photos via Ukraine authorities
Follow and listen to our podcast here