Oleh Kiper, writing on the Telegram messaging app, said the body of a man had been recovered from under rubble. Three people were taken to hospital with serious injuries.
"We have no certainty about the information from neighbouring residents and therefore can't be sure," Kiper told national television.
"So the search and clearing operation will continue until the last brick is removed to make sure no one is left there."
Pictures posted online showed flames reaching skyward from a number of buildings.
(Reporting by Ron Popeski and Nick Starkov; editing by Jonathan Oatis)
