Another body has been recovered from the ruins of a Florida condominium tower, raising the death toll in the collapse to at least 12, with 149 people still listed as missing.

The latest casualty of the disaster, which could ultimately rank as the worst accidental building collapse in US history, was not immediately identified, Miami-Dade County Mayor Daniella Levine Cava said on Tuesday (local time).

Authorities still hold out hopes that more survivors might yet be found in the rubble left when nearly half the 12-floor, 156-unit tower abruptly caved in on itself last week, but they are fading.

Families of those still missing were “coping with the news that they might not have loved ones come out alive and still hoping that they will”, Ms Levine Cava said earlier.

“Their loved ones may come out as body parts,” the mayor said.

Officials said late on Monday that teams picking through broken concrete, twisted metal and dust from pulverised building materials were still treating the round-the-clock operation – which has employed dog teams, cranes and infrared scanners – as a search-and-rescue effort.

But no one has been extricated alive from the ruins of the oceanfront Champlain Towers South condo in Surfside, adjacent to Miami Beach, since a few hours after one side of the building collapsed early last Thursday.

Miami-Dade Fire Rescue Chief Alan Cominsky said on Tuesday that personnel faced an enormous task while working 12-hour shifts in the heat.

“That building collapsed almost in a footprint of where that building stood – we’re talking about 12 storeys, with subterranean garages all within that same footprint,” he said.

“I’m sure to emphasise the magnitude of what we encountered, what we’re seeing.”

Rescue workers had moved more than 900 tonnes of concrete from the debris since the collapse, Chief Cominsky said. The teams include experts sent by Israel and Mexico.

US President Joe Biden and his wife, Jill Biden, will visit Surfside on Thursday, the White House said.

The disaster has sent officials in nearby areas scrambling to check the safety of buildings.

Florida prosecutors are pursuing an investigation into the deadly collapse, with State Attorney Katherine Fernandez Rundle saying she will bring the matter before grand jurors soon.

“I am going to urge them to take a look at it,” Ms Rundle told the Miami Herald.

Ms Levine Cava said “we will be fully on board” any grand jury investigation.

The 2018 engineer’s report warned of “major structural damage” to the concrete slab beneath the pool deck and deterioration, including exposed rebar, in the underground parking garage.

The report’s author, Frank Morabito, wrote the deterioration would “expand exponentially” if not repaired.

A lawyer who works with the condo association, Donna DiMaggio Berger, previously said the issues outlined in the 2018 report were typical for older buildings in the area.

-with AAP