Images from the scene showed lines of black body bags on the side of the road, while more bodies were seen wrapped in foil blankets among the debris.
Video footage also showed fire crews fighting to extinguish the shells of burned-out cars among the rubble from damaged buildings.
The dead included two children, the State Emergency Service of Ukraine said in a statement. A further 117 people were wounded, including 15 children, it said.
“Only filthy scum can act like this – taking the lives of ordinary people,” Ukrainian President Volodymyr Zelenskyy said.
In a statement on social media, he said the first strike hit buildings belonging to a city university, while the second exploded above street level.
Russia has yet to comment on the strike and it denied targeting civilians in previous attacks.
On Sunday, Russia’s defence ministry accused Ukraine of having carried out two attacks on Russian energy infrastructure over the previous day.
The attack on Sumy followed a deadly April 4 missile strike on Zelenskyy’s hometown of Kryvyi Rih that killed some 20 people, including nine children.
It comes a day after Russia and Ukraine’s senior diplomats accused each other of violating a tentative US-brokered deal to pause strikes on energy infrastructure, underscoring the challenges of negotiating an end to the three-year war. (AP)