Eighty-nine people, including 11 children, were also injured in the attack on the city late on Sunday, Ukraine's state emergency service said via Telegram.
The attack on Sumy followed a morning of Russia pounding Ukraine's power grid in what Kyiv said was a "massive" attack with 120 missiles and 90 drones that killed at least seven people.
The attack targeting Ukraine's energy infrastructure came as fears mount about Moscow's intentions to devastate Ukraine's power generation capacity before the winter.
It also followed President Joe Biden authorising for the first time the use of US-supplied long-range missiles by Ukraine to strike inside Russia after extensive lobbying by Ukrainian officials.
Hundreds of people were evacuated after the missile strike, which killed 11 people and injured 89. (EPA PHOTO)
"Sunday evening for the city of Sumy became hell, a tragedy that Russia brought to our land," Volodymyr Artyukh, the head of the Sumy military administration said in a post on the administration's Telegram messaging channel.
The military administration said another missile hit critical infrastructure, leaving the city without power.
Ukraine's air force said Russian forces used two Iskander-M ballistic missiles and a Kh-59 guided missile in the overnight attack.
Rescuers and all necessary services continued to work at the scene and psychologists were providing assistance to those affected, the State Emergency Service of Ukraine said on Telegram.
More than 400 people were evacuated, the Service said.
Photos show a multi-storey building with nearly windows blown out and its facade damaged. (EPA PHOTO)
Photographs posted on Telegram by State Emergency Service of Ukraine showed firefighters battling a blaze consuming cars and rescuers carrying people out of a building.
One image showed a multi-storey building with nearly all windows blown out and its facade damaged.
Sumy regional prosecutors said the attack damaged 90 apartments, 28 cars, two educational institutions and 13 buildings.
There was no immediate comment from Moscow.
Both sides deny targeting civilians in their strikes on each other's territory.
But thousands have died since early 2022 in Russia's full-scale invasion of Ukraine, the vast majority of them Ukrainians.
with AP
