Authorities in Florida have asked the federal government for an additional rescue team to comb the rubble of a collapsed condo tower in Surfside near Miami.

The possibility that severe weather in coming days could further stretch Florida's search and rescue resources prompted state officials to ask the federal government for the additional team, Kevin Guthrie of the Florida Division of Emergency Management said on Tuesday.

Already, intermittent bad weather has caused temporary delays in the search.

Mr Guthrie said the new team, which would likely come from Virginia, would be on hand if severe weather hits the area in coming days and allow crews that have been working at the site for days to rotate out.

Authorities said it is still a search-and-rescue operation, but no one has been found alive since hours after the collapse on Thursday.

Mr Guthrie said at a news conference: "There are two areas of (possible storm) development out in the Atlantic, heading to the Caribbean.

"We have eight urban rescue teams in Florida. We talked about doing a relief. We have all the resources we need but we're going to bring in another team. We want to rotate those out so we can get more resources out."

The National Hurricane Centre says two disorganised storm systems in the Atlantic have a chance of becoming tropical systems in the coming days, but it is unclear at this point whether they would pose a threat to the US.

Charles Cyrille of the Miami-Dade County Office of Emergency said 900 workers from 50 federal, state and local agencies were working seamlessly on the search.

Elected officials have pledged to conduct multiple investigations into the sudden collapse of the 12-storey Champlain Towers South in Surfside last week.

Another victim was recovered on Tuesday, bringing the confirmed death toll to 12, with 149 people still unaccounted for.

Miami-Dade County mayor Daniella Levine Cava said that she and her staff will meet with engineering, construction and geology experts, among others, to review building safety issues and develop recommendations "to ensure a tragedy like this will never, ever happen again".

State attorney Katherine Fernandez Rundle said she will pursue a grand jury investigation to examine factors and decisions that led to the collapse.

Governor Ron DeSantis evoked a well-known military commitment to leave no one behind on the battlefield and pledged to do the same for the people still missing in the rubble.

Mr DeSantis said at a news conference on Tuesday: "The way I look at it, as an old Navy guy, is when somebody is missing in action, in the military, you're missing until you're found. We don't stop the search."

Also on Tuesday, the White House announced that President Joe Biden and first lady Jill Biden would travel to Surfside on Thursday.

Work at the site has been deliberate and treacherous. The pancake collapse of the building left layer upon layer of intertwined debris, frustrating efforts to reach anyone who may have survived in a pocket of space.

Several members of an Israeli rescue team worked partly on hands and knees on Tuesday over a small section of the rubble, digging with shovels, pickaxes and saws.

They removed debris into buckets that were dumped into a metal construction bin, which was periodically lifted away by a crane. The crane then delivered an empty bin.

Late in the afternoon, rescue officials sounded a horn for a second time during the day's work, signalling an approaching storm with lightning. Workers temporarily evacuated.

Miami-Dade fire chief Alan Cominsky said the work has been extremely difficult, but "we're out here 110%".

He said: "These are the times that are the most difficult. We are here to do a job. We are here with a passion. Hopefully, we have some success."

Meanwhile, it has emerged that weeks before the building collapsed, the president of its board wrote a letter saying that structural problems identified in a 2018 inspection had "gotten significantly worse" and owners needed to pay a hefty price to get them fixed.

The April 9 letter from Champlain Towers South Condominium president Jean Wodnicki hinted at an ongoing debate over the repairs and a reluctance by some condo owners to pay for major work that would cost at least 15.5 million dollars.

"A lot of this work could have been done or planned for in years gone by. But this is where we are now," she wrote in the letter, which was confirmed to The Associated Press by a spokesman for the condo board.

Ms Wodnicki noted that costs had increased since an October 2018 report by engineering firm Morabito Consultants first identified key issues with weakening concrete, and she predicted they would only grow more if put off any longer.

"Indeed the observable damage such as in the garage has gotten significantly worse since the initial inspection," she wrote. "The concrete deterioration is accelerating."

"It is impossible to know the extent of the damage to the underlying rebar until the concrete is opened up. Oftentimes the damage is more extensive than can be determined by inspection of the surface."