Miami-Dade Mayor Daniella Levine Cava said the number unaccounted for has now dropped to 156, with three more of the recovered bodies identified.
“Our top priority continues to be search and rescue and saving any lives that we can,” she told reporters.
Part of the building collapsed early in the morning on Thursday while many residents slept.
The cause of the collapse remains unclear.
But an engineer’s report from 2018 was made public on Saturday, which highlighted “a major error” in the original design of the seafront Champlain Towers in the town of Surfside, near Miami. It said the fault prevented water draining away from the base of the building.
President Joe Biden tweeted that he had offered “assistance as needed” to Florida Governor Ron DeSantis.
Teams have been using machines, drones and specially trained dogs in their efforts to find survivors. Rescue efforts were briefly hampered on Saturday after a fire broke out underneath the rubble.
Ms Levine Cava said the death toll increased after emergency workers found a body in the rubble on Saturday. Four of the five confirmed fatalities have been identified – they include the mother of a boy who was pulled alive from the rubble on Thursday.
The Miami-Dade mayor said the search efforts had also uncovered some human remains, but warned that the process of identifying these victims was “very difficult” and would rely on DNA testing.
The missing include people from Israel and Latin America, according to reports. Paraguay’s foreign ministry said six of its nationals had been registered as missing, including the sister of the country’s first lady.
Local officials have provided families with hotel rooms and food as they wait for news about their loved ones.
What issues did the 2018 report raise?
The engineer, Frank Morabito, said the lack of proper drainage was “a systemic issue” that stemmed from a flaw “in the development of the original contract documents”.
He flagged what he called “major structural damage” to the concrete platform beneath the swimming pool deck.
“The failed waterproofing is causing major structural damage to the concrete structural slab below these areas,” he wrote. “Failure to replace the waterproofing in the near future will cause the extent of the concrete deterioration to expand exponentially.”
The engineer also referred to “abundant cracking… of columns, beams and walls” in the garage.
His report didn’t suggest the 40-year-old building was at any imminent risk of collapse but he urged that the concrete repairs be carried out in “a timely fashion”.
It is unclear if the problems highlighted contributed to the structural failure. Champlain Towers had been due to undergo a multi-million dollar refurbishment this year.
Morabito Consultants later issued a statement on Twitter, confirming they had written the report in 2018.
“At the time of the building collapse, roof repairs were underway, but concrete restoration had not yet begun,” the statement said. The firm does not perform any construction work but said it was brought in by the condominium association in June 2020 to prepare a repair and restoration plan.
Governor DeSantis has promised that authorities will find out what happened saying “anybody affected by this directly wants that answer”.
What happened to the building?
The building contained 136 apartments and 55 of them collapsed early on Thursday, leaving piles of debris.
Resident Barry Cohen was in bed in a section of the building that survived when the collapse happened. “It sounded like thunder, and my wife and I, we went out on the balcony; it looked like a bomb had exploded,” he told the BBC.
“When we opened the door, there was no building there, it was just a pile of rubble,” he said.
Eyewitnesses described hearing what sounded like thunder before seeing a huge cloud of dust in the aftermath of the collapse.
A full investigation into the collapse is set to begin after the rescue mission.
As the building has stood since 1980, it was due its standard 40-year review. It was undergoing its “recertification” process and required repairs, officials said.
A study from researchers at Florida International University published last year found that the building had been sinking at a rate of two millimetres per year in the 1990s, which may have affected the building structurally.
But the author has cautioned that the study was just a snapshot in time. The building was constructed on reclaimed wetland, which experts say is always of concern as the land underneath can compact over time, leading to shifts.
On the sinking, the author of the study, Prof Shimon Wdowinski, told the Miami Herald newspaper: “We’ve seen much higher than that, but it stood out because most of the area was stable and showed no subsidence.”
Prof Wdowinski said the research was not meant to suggest certainty about the latest incident.