Florida building collapse: The death toll has risen to five after the collapse of an apartment block in Florida, authorities say

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.

Florida building collapse: The death toll has risen to five after the collapse of an apartment block in Florida, authorities say

As yet 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. 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.

"My heart is with the community of Surfside as they grieve their lost loved ones and wait anxiously as search and rescue efforts continue," he posted.

My heart is with the community of Surfside as they grieve their lost loved ones and wait anxiously as search and rescue efforts continue.

Yesterday I spoke with Gov. DeSantis to let him know that we are ready to provide assistance as needed by state and local officials.

— President Biden (@POTUS) June 26, 2021

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.

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 relatives 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.

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.