Rescue teams were using cranes, dogs and infrared scanners to identify signs of life in the ruins, although hope was diminishing as time wore on.   

Search and rescue teams discovered two more bodies the concrete and steel rubble of a collapsed Florida condominium tower on Monday, bringing the death toll to 11 with 150 people still considered missing.

Recovery efforts were hampered by pouring rain and heavy slabs of cement that made searching by hand difficult.

It has now been four days since a survivor was pulled alive from the ruins of the Champlain South Towers in Surfside, Florida, which abruptly collapsed on Thursday while most residents slept.

"We have people waiting and waiting and waiting. That is excruciating," Miami-Dade County Mayor Daniella Levine Cava told an afternoon news briefing, referring to friends and family members of the missing or dead.

"They are coping with the news that they might not have loved ones come out alive and still hoping that they will," the mayor said. "Their loved ones may come out as body parts."

Rescue teams were using cranes, dogs and infrared scanners to identify signs of life in the ruins, although hope was diminishing as time wore on.

Some relatives of the missing have provided DNA samples to officials. Family members were permitted to visit the site on Sunday.

Miami-Dade Assistant Fire Chief Raide Jadallah said workers have found voids large enough to keep victims alive.

"Not to say that we have seen 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, that could possibly be made by a survivor, although he acknowledged that they could also be caused by shifting metal.

The search teams include experts sent by Israel and Mexico.

The cause of the collapse remains under investigation.

REPORT WARNED OF TROUBLE

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 ... 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.

The engineer's report was commissioned as the condo, which was built in 1981, sought recertification, which is required for buildings 40 years old. An estimate prepared by Morabito Consultants in 2018 put the cost of repairs at US$9.1 million.

Guillermo Olmedillo, Surfside's town manager in 2018, told Reuters he did not recall hearing about structural issues.

"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 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.

Police have identified eight of the deceased, 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 dead 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 US history.

Ninety-eight people died when the roof of the Knickerbocker Theatre in Washington, D.C., gave way from the weight of snow during a movie screening in January 1922.

Two interior walkways collapsed into the lobby of the Hyatt Regency hotel in Kansas City, Missouri, during a party in July 1981, killing 114.

Reuters