Rescue operations have stretched into a second day at a Kyiv children’s hospital which was struck by a Russian missile as Ukrainian officials raised the countrywide death toll to 42 after the intense daytime attack on multiple cities.

Mr Zelensky said on the social platform X that 64 people were taken to hospital in the capital as well as 28 in Kryvyi Rih and six in Dnipro — both in central Ukraine.

It was Russia’s heaviest bombardment of Kyiv in almost four months and one of the deadliest of the war, hitting seven of the city’s 10 districts.

The strike on the Okhmatdyt children’s hospital, which interrupted open-heart surgery and forced young cancer patients to have their treatments outdoors, drew an international outcry.

The 10-storey hospital, which is Ukraine’s largest medical facility for children, was caring for 670 patients at the time of the attack, Okhmatdyt’s director general Volodymyr Zhovnir said on Tuesday. The missile hit a two-storey wing of the hospital.

“The building where we conducted dialysis for children with kidney failure or acute intoxication is ruined entirely,” he told reporters, estimating the overall damage to the hospital at 2.5 million dollars.

Danielle Bell, the head of a UN team tracking human rights violations in Ukraine, said at least two people were killed at the hospital and some 50 people were injured, including seven children.

The casualty figure would have been much higher if patients had not been taken to a bunker when air raid sirens first sounded, she added.

Mr Zhovnir said one of the two killed at the hospital was a female doctor who took children to the shelter and then went back to check nobody had been left behind

Oleh Holubchenko, a paediatric surgeon at the hospital, was operating on a baby with congenital face defects. Despite the sound of air sirens, he and his team decided to continue with the operation. “We couldn’t stop halfway through,” he told The Associated Press.

Rescuers search through rubble
A major Russian missile attack across Ukraine killed at least 20 people and injured more than 50 (AP)

When the missile struck, the shock wave flung him across the operating theatre. Shrapnel caused him minor injuries and pierced the infant’s ventilator. The baby, still with an open wound, had to be transported to another Kyiv hospital where they finished the surgery.

Authorities are working to restore the hospital’s power and water supply.

It was Russia’s heaviest bombardment of Kyiv in almost four months and one of the deadliest of the war, hitting seven of the city’s 10 districts.

The strike on the Okhmatdyt children’s hospital, which interrupted open-heart surgery and forced young cancer patients to take their treatments outdoors, prompted an international outcry.

Kyiv city administrators declared Tuesday an official day of mourning. Entertainment events were prohibited and flags lowered in the capital.

Russia denied responsibility for the hospital strike, insisting it does not attack civilian targets in Ukraine despite abundant evidence to the contrary.

Kremlin spokesman Dmitry Peskov on Tuesday repeated that position, pointing to a Russian Defence Ministry statement that blamed a Ukrainian air defence missile for partially destroying the hospital.

Rescuers work in the rubble
A number of children were injured (AP)

The Russian onslaught came on the eve of a Nato summit in Washington where alliance countries are expected to pledge new military and economic support for Ukraine.

Meanwhile, Russian President Vladimir Putin is hosting India’s Prime Minister Narendra Modi in Moscow.

New Delhi’s importance as a key trading partner has grown since the Kremlin sent troops into Ukraine in February 2022.

Mr Zelensky was deeply critical of Mr Modi’s visit, saying on X late on Monday: “It is a huge disappointment and a devastating blow to peace efforts to see the leader of the world’s largest democracy hug the world’s most bloody criminal in Moscow on such a day.”