Fire and smoke coming from deep inside the concrete and metal remains of a collapsed 12-story condominium tower near Miami hampered rescue efforts Saturday as emergency workers raced to recover any survivors beneath the mountain of rubble.

Rescuers used infrared technology, water and foam to battle the blaze, whose source was unclear, and Miami-Dade Mayor Daniella Levine Cava said the smoke has been the biggest challenge. In a news conference, she described the blaze as “very deep” and said rescuers faced “incredible difficulties” because of the flames.

A firehose blasted one of the lower floors on the north side of the tower as white smoke or steam streamed out, and a bitter, sulfur-like smell hung in the air.

“The stench is very thick,” Florida Gov. Ron DeSantis said.

A crane removed pieces of debris from the more than 30-foot pile, and scores of rescuers used big machines, small buckets, drones, microphones and their own hands to pick through the rubble.

Among those anxiously awaiting word of missing loved ones was Rachel Spiegel, whose mother, 66-year-old Judy Spiegel, lived on the sixth floor. Speaking alongside her siblings, she said Saturday that “we’re trying to hold it together.”

“I know my mom is a fighter. I know she loves us. I know she doesn’t want to give up. So, you know, it’s day three, so it’s hard,” Spiegel said.

One hundred fifty-nine people were still unaccounted for two days after Thursday’s collapse, which killed at least four.

Authorities announced they are beginning an audit of buildings nearing their 40-year review — like the fallen Champlain Towers South — to make sure they’re safe. The mayor asked other cities in the county to join the building review and said there will be state and federal funding to help.

Federal Emergency Management Agency officials have joined local and state authorities at the site, DeSantis said. He added that a nearby “sister building” of the collapsed tower is also being looked at because it was built at the same time and with the same designer.

Surfside Mayor Charles Burkett said he was working on a plan to temporarily relocate residents of the Champlain Towers North, which was constructed the same year and sits about 100 yards away from the collapsed building, and that FEMA has agreed to pay for lodging.

Burkett added that he was also trying to arrange an emergency inspection and until that happens, he can’t tell residents whether they’re safe in their homes.

“I know that the identical building collapsed for an inexplicable reason,” Burkett said. “Buildings in the United States do not just fall down. … Something very, very wrong was going on at that building, and we need to find out.”

The mayor said he didn’t plan to order residents to evacuate, but if he lived there, “I’d be gone.”

Surfside city staffers were also gathering details about a third building, Champlain Towers East, which was built in a different style and appears to have been constructed at a different time.

The news came after word of a 2018 engineering report that showed the building 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.

The report from the firm of Morabito Consultants did not warn of imminent danger from the damage, and it is unclear if any of the damage observed was responsible for the collapse. But the report noted the need for extensive and costly repairs to fix systemic issues with the building.

It said the waterproofing under the pool deck had failed and had been improperly laid flat instead of sloped, preventing water from draining off.

The firm recommended that the damaged slabs be replaced in what would be a major repair.

The report also uncovered “abundant cracking and spalling” of concrete columns, beams and walls in the parking garage. Some of the damage was minor, while other columns had exposed and deteriorating rebar. It also noted that many of the building’s previous attempts to fix the columns and other damage with epoxy were marred by poor workmanship and were failing.

Beneath the pool deck “where the slab had been epoxy-injected, new cracks were radiating from the originally repaired cracks,” the report said.

Gregg Schlesinger, a former construction project engineer who is now a lawyer handling construction defect cases, said another area of concern in the report is cracks that were discovered in the tower’s stucco facade. Schlesinger said that could indicate structural problems inside the exterior that could have been critical in the collapse.

“The building speaks to us. It is telling us we have a serious problem,” Schlesinger said in a phone interview Saturday.

He added that there are frequently “telltale signs” on oceanfront buildings indicating problems structurally largely from saltwater and salty air intrusion.

“This is a wakeup call for folks on the beach. Investigate and repair. This should be done every five years,” Schlesinger added. “The scary portion is the other buildings. You think this is unique? No.”

A crane could be seen removing pieces of rubble from a more than 30-foot pile of debris at the collapse site. Scores of rescuers used big machines, small buckets, drones, microphones and their own hands to pick through the rubble.

While officials said no cause for the collapse early Thursday has been determined, DeSantis said a “definitive answer” was needed in a timely manner. Video showed the center of the building appearing to tumble down first, followed by a section nearer to the beach.

The 2018 report was part of preliminary work by the engineering company conducting the building’s required inspections for a recertification due this year of the building’s structural integrity at 40 years. The condominium tower was built in 1981.

(AP)