The crews were using cranes, dogs and infrared scanners to identify signs of life in the ruins, hoping survivors could still be alive in air pockets under the rubble.
"We're going to continue and work ceaselessly to exhaust every possible option in our search," Miami-Dade County Mayor Daniella Levine Cava told reporters at a news briefing. She acknowledged the number of casualties could rise, with 151 people still considered missing.
Miami-Dade Assistant Fire Chief Raide Jadallah said workers have found voids large enough to keep victims alive.
"Not to say that we have see anyone down there, but we've not gotten to the very bottom," he said.
Jadallah said searchers have heard some sounds, such as tapping or scratching, although he acknowledged that they could be caused by metal shifting. He said there was no set time to stop rescue operations.
The teams include experts sent by Israel and Mexico to assist in the search.
The cause of the collapse at the Champlain Towers South in Surfside, near Miami, remains under investigation.
A 2018 engineer's report found serious concrete deterioration in the underground parking garage and major damage in a slab beneath the pool deck. The report's author, Frank Morabito, wrote that the deterioration would "expand exponentially" if not repaired.
Ross Prieto, then Surfside's top building official, met residents the following month after reviewing the report and assured them the building was "in very good shape," according to minutes of the meeting released on Monday. After the meeting, Prieto emailed the town's manager to say it "went very well. The response was very positive from everyone in the room. All main concerns over their forty year recertification process were addressed."
Reuters was unable to reach Prieto, who is no longer employed by Surfside. He told the Miami Herald newspaper he did not remember getting the report.
'FAILURE TO ACT'
The engineer's report was commissioned in advance of the condo seeking recertification, which is required for buildings 40 years after they are constructed. The tower was built in 1981. An estimate prepared by Morabito Consultants in 2018 put the cost of repairs at $9.1 million, including electrical, plumbing and work on the facade.
Guillermo Olmedillo, Surfside's town manager in 2018, told Reuters he did not recall hearing about structural issues in the tower based on the engineer's report.
"The last thing I knew was that everything is OK, reported by the building official," Olmedillo said.
Gregg Schlesinger, a lawyer and former general contractor who specializes in construction-failure cases, said it was clear the deficiencies identified in the 2018 report were the main cause of the disaster.
But Donna DiMaggio Berger, a lawyer who works with the condo association, said the issues were typical for older buildings in the area and did not alarm board members, all of whom lived in the tower with their families.
Morabito Consultants said on Saturday that roof repairs were under way at the time of the collapse, but concrete restoration had not yet started.
"We are deeply troubled by this building collapse and are working closely with the investigating authorities to understand why the structure failed," the firm said.
Some relatives of the missing have provided DNA samples to officials. Family members were permitted to visit the site on Sunday.
Over the weekend, a resident filed a lawsuit against the Champlain Tower South Condominium Association, accusing it of failure to act despite warnings that the building was structurally flawed.
The resident, Steve Rosenthal, said the association had “breached all of the contractual duties of care pertaining to the timely maintenance and repair of the structure of the condominium building.”
Police have identified eight victims, including a couple married for nearly 60 years and a mother whose teenage son is one of the few known survivors.
At a makeshift memorial a block away, tributes to the victims and "missing" posters hung on a chain-link fence, with flowers and children's toys strewn about.
Given the scores of those still missing, the disaster may end up as one of the deadliest non-deliberate structural failures in U.S. history.
Ninety-eight people perished when the roof of the Knickerbocker Theatre in Washington, D.C., gave way from the weight of snow during a silent movie screening in January 1922.
Two interior walkways collapsed into the lobby of the Hyatt Regency hotel in Kansas City, Missouri, during a dance party in July 1981, killing 114.