The grim, painstaking search for victims in the rubble, which was suspended for most of Thursday over safety concerns, proceeded on Friday with greater caution and a watchful eye on a hurricane that could strike Florida within days.

There are 128 people still missing and feared buried beneath tonnes of pulverised concrete, twisted metal and splintered lumber as the search stretched into its ninth day.

The number of people unaccounted for dropped by 17 from Thursday's figure.

Miami-Dade Mayor Daniella Levine Cava told a news briefing that the totals were fluid, in part because investigators sometimes learned of additional family members when determining whether missing residents were safe.

The young girl was the third child to be recovered from the collapse site in the oceanfront town of Surfside, next to Miami Beach.

Levine Cava said the discovery was especially difficult for rescuers, who have mounted an unprecedented around-the-clock effort to search for survivors even as the odds have grown longer with each passing day.

"Every victim we remove is very difficult," Miami-Dade County Fire Chief Alan Cominsky said.

"Last night was even more, when we were removing a fellow firefighter's daughter. As firefighters, we do what we do - it's kind of a calling. But it still takes a toll."

No one has been pulled alive from the debris since the initial hours after the 12-floor Champlain Towers South condo partially caved in on itself early on June 24 as residents slept.

Authorities had halted the rescue and recovery effort early on Thursday after they detected movement that raised concerns a section of the high-rise tower still standing might topple onto search crews in the debris field.

But the operation was restarted about 15 hours later when it was deemed safe although with a new set of precautions in place, Cominsky told reporters on Thursday evening.

Under the new search plan, teams would confine their work for now to just three of nine grids demarcated in the ruins of the 12-floor Champlain Towers South condo, Cominsky said.

At some point, the remaining part of the building will be demolished but Levine Cava said on Friday that it would "take some time" before that occurs.

Authorities were eager to make as much progress as possible before the expected arrival of Elsa, which strengthened into the first hurricane of the 2021 season on Friday as it threatened the Caribbean.

The storm could be near South Florida by Monday or Tuesday, National Weather Service meteorologist Robert Molleda told reporters, with tropical storm-force winds arriving as early as Sunday.

But he warned that Elsa's forecasted path remains uncertain.

The renewed search effort began shortly after a visit to the scene on Thursday by US President Joe Biden, who spent about three hours consoling families of the dead and missing.

Investigators have not determined what caused the 40-year-old condo complex to crumble into a heap in one of the deadliest building collapses in US history.

Australian Associated Press