Surfside Mayor Charles Burkett said construction work was being done on the roof but there was no indication it caused the collapse.
He added: “It’s hard to imagine how this could have happened. Buildings just don’t fall down.”
Daniella Levine Cava, Miami-Dade County Mayor, told reporters 99 people remained unaccounted for18 hours after the collapse, though some may not have been in the building at the time.
Another 102 individuals whose whereabouts were initially unknown have since been located and “declared safe,” she said.
A fire official said 35 people were evacuated from the part of the high-rise left standing.