As the death toll rose to nine, searchers worked on Sunday to find more than 150 missing residents amid the rubble of a Florida apartment building that collapsed three days ago, as questions arose about the tower's structural integrity.

The death toll was certain to rise as emergency workers in Surfside, a shore town near Miami, were joined by teams from Israel and experts from Mexico.

"Everybody that is needed is on the site and doing the work and we're continuing our efforts to find people alive," Miami-Dade County Mayor Daniella Levine Cava told CBS on Sunday.

Officials said they harbored hope that some of the 156 people unaccounted for might be alive. Aided by dogs, sonar, drones and infrared scanning, they hope people can survive in air pockets that may have formed in the debris.

A smoldering fire beneath the rubble that produced thick smoke and hindered the work of rescuers has abated, officials said. A trench was dug to separate the areas of smoking debris from the rest of the rubble and rescuers are also using tunnels, Levine Cava said.

"The biggest thing now is hope," Fire Chief Alan Cominsky said. "That's what's driving us. It's an extremely difficult situation."

Some families of those missing have provided DNA samples to officials while others recounted narrow escapes. Police released the names of four victims who ranged in age from 54 to 83.

Champlain Towers South resident Erick de Moura was supposed to be home when the building collapsed, but his girlfriend persuaded him to spend the night at her place less than 2 miles (3 km) away in Miami Beach, likely saving his life.

"Only by God. To me this is a miracle," the 40-year-old Brazil native told Reuters.

Photographs of the missing were posted on a nearby fence, along with flowers and messages. On Saturday, family members prayed and kept a silent vigil at a barrier erected on the beach by authorities several hundred yards north of the building site. They declined to comment.

Some residents remain in the sister building to the one that collapsed, where only a voluntary evacuation order has been issued. A building inspector did not find any immediately obvious problems with the other building.

"Having said that, I don't know if I'd be comfortable staying in that building," Surfside Mayor Charles Burkett said, until a comprehensive review was completed.

Officials said on Saturday that Miami-Dade County would audit all buildings more than 40 years old within the next 30 days to ensure their safety.

Surfside officials have released documents including an engineer's report from 2018 that found major structural damage beneath the pool deck and "concrete deterioration" in the underground parking garage of the 12-story condominium.

The report was produced for the Champlain Towers South condominium board in preparation for a major repair project set for this year.

It was not immediately clear whether the damage described in the report was connected to the collapse about 1:30 am (0530 GMT) on Thursday.

Donna DiMaggio Berger, a lawyer who works with the condo association, said the issues outlined in the 2018 report were typical for older buildings in the area and did not alarm board members, all of whom lived in the tower with their families.

The report estimated it would cost $9.1 million to make the recommended repairs. Berger said the board had taken out a $12 million line of credit to pay for the repairs and asked owners to pay $80,000 each. Work had started on replacing the roof ahead of hurricane season and the board was gathering bids for the concrete work, but the pandemic slowed the project, she said.

Satellite data from the 1990s showed the building was sinking 1 to 3 millimeters per year, while surrounding buildings were stable, according to Florida International University professor Shimon Wdowinski.

Gregg Schlesinger, a lawyer and former general contractor who specializes in construction-failure cases, said other factors could have contributed to the collapse, but it was clear to him that the structural issues identified in the 2018 report were the main cause.

He said investigations and the inevitable lawsuits will eventually paint a full picture of what caused the disaster.

"But we do know one thing: there was a structural failure," he said. "We know another thing: The structural failure should not have occurred."

He said all seaside buildings in the area should be inspected every five years to ensure they have not been degraded by the corrosive salt air, not just those over 40 years old.