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(MIAMI) — At least four people are dead and 159 others are unaccounted for after a 12-story residential building partially collapsed in southern Florida’s Miami-Dade County early Thursday, officials said.

“Tragically, I woke up to learn that three bodies had been pulled from the rubble last night. Devastating news for families waiting for any hope of survival,” Miami-Dade County Mayor Daniella Levine Cava told ABC News’ Cecelia Vega in an interview Friday on Good Morning America.

“Those three people have not been identified at this time,” she noted. “It does bring our count to four of those who have lost their lives in this tragedy.”

The first death was confirmed early Thursday, just hours after the partial collapse occurred at the Champlain Towers South condominium in the small, beachside town of Surfside, about 6 miles north of Miami Beach. The oceanfront complex has 136 units, and approximately 55 of them were destroyed along the northeast corridor, according to Miami-Dade Fire Rescue Assistant Chief Raide Jadallah.

A massive search and rescue operation has been underway since then, as crews carefully comb through the pancaked wreckage and remaining structure in hopes of finding survivors. So far, they have rescued 35 people who were trapped in the building and two others from beneath the rubble, according to Jadallah.

Footage from the scene showed firefighters pulling a boy from the rubble alive and rescuing others from still-standing balconies.

Jadallah told reporters that at least 11 people were medically assessed and treated on site, four of whom were then transported to local hospitals.

Meanwhile, the number of people who have been accounted for has gone up to 120, according to Levine Cava, who cautioned that the numbers are “very fluid.”

“We will continue search and rescue because we still have hope that we will find people alive,” Levine Cava said during a press conference in Surfside on Friday morning. “That is exactly why we are continuing.”

Some 130 firefighters have been taking part in the search and rescue efforts, cutting through the layers of debris with various machinery and using sonar devices as well as specially trained dogs. First responders have not heard any voices coming from the pile but have continuously picked up sounds, according to Jadallah.

“It’s not necessarily human sounds,” Jadallah said during a press conference in Surfside on Friday morning. “It could be various things. It could be just steel twisting, it could be debris raining down.”

“We have hope,” he added, “and every time that we hear a sound, we concentrate on that area.”

The remaining structure that still stands has been cleared by the rescue crews and all resources have now shifted focus to the rubble, according to Jadallah.

A Miami-Dade county official told ABC News that there’s real concern about the structural integrity of the remaining building, particularly from dangling wires and portions of concrete. Fires have flared up throughout the day, adding to the danger for the search and rescue teams, according to the official.

Levine Cava said there are trained experts, including structural engineers, on site to help keep rescuers safe while they search for survivors but that there is still “extreme risk.”

“Debris is falling on them as they do their work,” she told reporters Friday. “But they are proceeding because they are so motivated and they are taking extraordinary risk on the scene every day.”

Jadallah said it’s a risk that they are willing to take if it means finding people alive.

“It’s the risk versus benefit,” he told reporters Friday. “Every time we have that belief, that there’s hope, you know, with personnel that are trapped, we do risk our lives.”

President Joe Biden subsequently approved an emergency declaration in Florida and ordered federal assistance to supplement state and local response efforts in the wake of the partial building collapse. The action authorizes the U.S. Department of Homeland Security and the Federal Emergency Management Agency “to coordinate all disaster relief efforts which have the purpose of alleviating the hardship and suffering caused by the emergency on the local population, and to provide appropriate assistance for required emergency measures, authorized under Title V of the Stafford Act, to save lives and to protect property and public health and safety, and to lessen or avert the threat of a catastrophe in Miami-Dade County,” according to a statement from the White House.

“Specifically, FEMA is authorized to identify, mobilize, and provide at its discretion, equipment and resources necessary to alleviate the impacts of the emergency,” the statement noted.

Levine Cava told ABC News that she’s “grateful” to the president.

“He called me yesterday morning and asked me what I needed. I told him FEMA would be a great to assist to us and he moved mountains,” she said.

The Miami-Dade Fire Rescue is now pulling additional resources from FEMA to assist with the search and rescue efforts, Jadallah told reporters Friday morning.

The cause of the partial collapse remains unknown. The Miami-Dade Police Department is leading an investigation into the incident.

So far, there is no evidence of foul play, according to Levine Cava.

“Of course, it’s not ruled out,” she told ABC News on Friday. “Nothing’s ruled out. But, at this point, nothing to indicate that.”

The Champlain Towers South condominium was built in the 1980s and was up for its 40-year recertification, according to Surfside officials. The roof was also undergoing work and the entire building had been under scrutiny due to potential construction projects nearby, officials said.

The Champlain Towers South Condo Association was preparing to start a new construction project to make updates and the condominium had been through extensive inspections, according to Kenneth Direktor, a lawyer for the association. Direktor said the construction plans had already been submitted to the Town of Surfside but the only work that had begun was on the roof.

Direktor noted that he hadn’t been warned of any structural issues with the building or about the land it was built on. He said there was water damage to the complex, but that is common for oceanfront properties and wouldn’t have caused the partial collapse.

“Nothing like this has ever been seen, at least not in the 40 years I’ve been doing this,” Direktor told ABC News during a remote interview on Thursday.

Public records show a lawsuit was filed in 2015, claiming an outside wall of the Champlain Towers South had water damage and cracks. Engineers were hired to go through the inspection process, according to Direktor.

“Nothing like this was addressed to the board or the owners as an existing risk,” he said.

A 2020 study conducted by Shimon Wdowinski, a professor at Florida International University’s Institute of Environment in Miami, found signs of land subsidence from 1993 to 1999 in the area where the Champlain Towers South condominium is located. But subsidence, or the gradual sinking of land, likely would not on its own cause a building to collapse, according to Wdowinski, whose expertise is in space geodesy, natural hazards and sea level rise.

“When we measure subsidence or when we see movement of the buildings, it’s worth checking why it happens,” Wdowinski, who analyzed space-based radar data, said in a statement Thursday. “We cannot say what is the reason for that from the satellite images but we can say there was movement here.”

Areas where land is subsiding are more likely to experience more serious effects of sea level rise, according to the study, which was published in the international journal Ocean & Coastal Management.

Miami-Dade County officials are aware of the study and are “looking into” it, Levine Cava told ABC News.

Greg Batista, president of G. Batista Engineering and Construction in Davie, Florida, told ABC News that he worked on the planters at the Champlain Towers South in 2017 and was among the structural engineers on scene after the partial collapse early Thursday. He said he has not heard of any structural issues with the Champlain Towers South.

“It’s just … bizarre for me to see what happened here because of the rarity of something like this happening,” Batista told ABC News during a remote interview Thursday.

John Pistorino, a longtime structural engineer in Miami who helped write Florida’s building codes, told Tequesta ABC affiliate WPBF that he has been hired to help investigate what caused the partial collapse and said it could take “months.” Once search and rescue efforts have finished, the structure will be dismantled and the debris will be looked at “piece by piece,” he said.

Investigators will also look at any reports on the building and may send samples from the site to a laboratory for testing, according to Pistorino.

When asked what could have led to the partial collapse, he said “it could be a number of issues.”

“There’s just too many issues for me to even begin to come up with a laundry list of possibilities that would be informative,” Pistorino told WPBF during a telephone interview Thursday. “I’m just surprised that it happened to begin with.”

A “substantial number” of the Champlain Towers South residents are from overseas and “almost a third” of those reported missing are foreign citizens, according to Florida Sen. Marco Rubio.

“We are working with the Consulates of various countries in the Western Hemisphere to help secure travel visas for family members who need to travel to the U.S.,” Rubio wrote in a post on his official Twitter account on Thursday evening.

Paraguay’s foreign ministry said that six Paraguayan nationals were in the building and are still missing: Sophia López-Moreira, the sister of the country’s first lady; her husband, Luis Pettengill; their three children; and their nanny, Lady Luna Villalba. Paraguayan President Mario Abdo Benítez canceled his events due to the incident.

Meanwhile, Argentina’s consulate in Miami said that nine Argentine nationals are missing. Venezuela’s ambassador to the United States confirmed that four Venezuelan nationals are missing. Uruguay’s foreign ministry said that three Uruguayan nationals have been affected by the incident, though their status was unclear. Colombia’s foreign ministry also reported that six Colombian nationals resided in the condominium and officials were still trying to determine whether they were there at the time of the collapse.

A Miami-Dade County official told ABC News it’s been difficult to determine how many people were in the collapsed section of the building, partly due to the fact that there isn’t an on-scene management company that keeps track. The condominium is a mix of full-time residents, seasonal residents, renters and short-term visitors, so authorities have been relying largely on neighbors and word of mouth, according to the official.

Authorities have opened a family assistance center at the Surfside recreational center for individuals unable to locate loved ones who live in the Champlain Towers South. Anyone with family members from the condominium who are either safe or still missing is urged to call 305-614-1819 to account for them.

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