The number of people confirmed to have been killed in the collapse of a Miami-area condominium tower last month has reached 86, Miami-Dade County Mayor Daniella Levine Cava said on Saturday.

No survivors have been pulled alive from the ruins.

Investigators have not determined what caused the 40-year-old complex to collapse.

"It is a staggering and heartbreaking number that affects all of us very, very deeply," said the county mayor. 

Champlain Towers South, a 12-story building in Surfside, a town north of Miami Beach, came tumbling down on June 24, as residents slept inside.