The official death toll in the Miami-area condominium collapse rose to at least nine people, officials announced Sunday morning, as rescue crews supplemented by federal and state resources, as well as teams from Mexico and Israel, continued to search through the rubble. 

The mayor of Surfside, Fla. stressed Sunday that the first priority of rescue crews is to find those some 152 building occupants who remain unaccounted for and reunite them with their families – as the cause of the 12-story building collapse remains unclear four days later. Alternate housing will be provided for residents in a sister building as an "army of engineers" is set to set to begin a "top to bottom" review of its infrastructure. 

"Our first priority and our only priority is to pull our residents out of that rubble and reunite them with their family who are understandably out of their minds with emotion, sadness, anger and just confused and want to know what’s happening," Surfside Mayor Charles Burkett told ABC's "This Week." "Our duty is to continue to do our jobs, which is to find their loved ones and reunited them." 

What caused Champlain Towers South to collapse remains unclear, though Burkett, speaking to ABC, compared the 30-foot pile of pancaked concrete and mangled metal that rescuers continued to comb through for survivors as similar tedious rescue efforts that happened after the 2001 terrorist attack on the World Trade Center in New York City. 

FLORIDA GOV. DESANTIS: MIAMI SISTER BUILDING OF COLLAPSED CONDO MAY HAVE TO BE EVACUATED 

"Buildings don’t fall down in America. That is a third-world phenomenon," Burkett said. "The last time we saw something like this -- well we had two sections of building fall down pancake style separately, and then you saw the fire. It’s very reminiscent of something we’ve seen in New York. It’s very disturbing. There was something obviously very, very wrong in this building and we need to get to the bottom of it." 

Meanwhile, residents of the sister building, Champlain Towers North, which Burkett said "was built around same time by same contractor with same plans and probably with the same materials," will be provided alternate housing as a "top to bottom" investigation is set to begin next week. 

"We don’t know why that building fell down and we need to get in and understand what’s going on with the sister building," the mayor said. "We are going to make alternate housing available for any resident who really doesn’t want to be in that building pending that investigation which is going to commence next week with what I would say an army of engineers to get in there and pour over that building from top to bottom." 

Speaking earlier Sunday on Fox & Friends, Burkett said he walked the site of the building collapse that morning and has seen "substantial progress" since Saturday afternoon, pointing out that despite complications caused by heavy rains overnight "that hasn’t stopped the waves and waves of rescue people here on sight all the way from Mexico and even Israel to pull our residents out of this rubble." 

"The water is probably helpful for people waiting to be extracted from the rubble, but at the same time, the fire that we had for several days was not welcome," Burkett said, explaining how first a fire that blazed beneath the rubble for days caused complications for rescue crews before the rain came.

The mayor praised the fire department for its "fabulous job" in getting the fire under control, adding that "We are 100% full speed working to pull everybody out of that pile of rubble." 

"We don’t have a resource problem, we have a luck problem," Burkett told Fox & Friends. "We’ve had the fire, we’ve had the weather. But the logistics -- we’ve had support from the White House, our two Florida senators, our fantastic governor, our fantastic county mayor. We don’t have resource problem, we just have a luck problem. We need a little more luck. We gotta get lucky." 

As scores of rescuers continued to use heavy machinery and power tools to clear the rubble from the top and tunnel in from below, some 200 family members of those who were inside the building at the time of the collapse remain at a nearby hotel ballroom, where they’ve periodically been briefed by officials and expressed frustration about the pace of recovery efforts. 

Sen. Marco Rubio, R-Fla., told CBS’ "Face the Nation" that those residents in the twin building have been made "FEMA eligible," meaning if they would like to relocate, the Federal Emergency Management Agency will help them with those arrangements. 

A team has come from Washington, D.C. under the Department of Commerce that specializes in "massive, catastrophic structural failures" to help local authorities identify what needs to be preserved for a full-scale investigation, he said. 

"I have little doubt that we will know why this happened and be able to make changes to building codes if necessary to prevent it from happening again. But right now, 99% of the focus is on trying to find any survivors and give these families closure on this terrible tragedy," he added. 

Rubio said the U.S. Army Corps of Engineers has sent some engineers to do a preliminary assessment of the building that is still standing and those immediately alongside the collapsed complex to make sure that additional collapses don't happen during the search process. He said some rescuers were in Haiti after a recent earthquake and had been able to pull some survivors out of the rubble there almost a week and a half after that disaster.  

The confirmed death toll had risen to five Saturday as rescuers battled fire and smoke deep inside the heap in a race against time. With a sulfur-like stench hanging in the air, they used everything from trained dogs and sonar equipment to buckets and drones.

Miami-Dade Mayor Daniella Levine Cava said the identification of three bodies had dropped the number of people unaccounted for down to 156, and crews also discovered other unspecified human remains. The remains are being sent to the medical examiner, and authorities are gathering DNA samples from family members to aid in identification.

Also late Saturday, Burkett said a city official had led a cursory review of the nearby Champlain Towers North and Champlain Towers East buildings but "didn’t find anything out of the ordinary."

The news came after word of a 2018 engineering report that showed the building, which was built in 1981, had "major structural damage" to a concrete slab below its pool deck that needed extensive repairs, part of a series of documents released by the city of Surfside.

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Further documentation showed the estimated cost of the repairs would total over $9 million. That included more than $3.8 million for garage, entrance and pool remediation and nearly $3.2 million for fixes to the exterior façade.

While officials said no cause for the collapse has been determined, Florida Gov. Ron DeSantis said a "definitive answer" was needed in a timely manner.

The Associated Press contributed to this report. 

Danielle Wallace is a Digital Reporter for Fox News and FOX Business. Follow her on Twitter at @danimwallace. If you've got a tip, you can email her at danielle.wallace@fox.com.