Rescue efforts at the site of a partially collapsed Florida condominium building resumed Thursday evening, about 15 hours after the work was halted out of concern about the stability of the remaining structure, the mayor said.

Surfside Mayor Charles Burkett said he did not know why officials decided to restart the search. Rescuers left the pile of rubble shortly after 2 a.m. after crews noticed widening cracks and up to a foot of movement in a large column.

"Finding missing loved ones continues to be at the forefront of our operations,” Miami-Dade Fire Rescue tweeted soon after search efforts resumed.

The stoppage threatened to keep search teams off the rubble pile and dim hopes for finding anyone alive in the debris a week after the tower came down.

The rescue operations unfolded on the same day that President Joe Biden and first lady Jill Biden visited the devastated community.

The collapse of the 12-story Champlain Towers South beachfront condominium killed at least 18 people and left 145 missing. Hundreds of search-and-rescue personnel have painstakingly searched the pancaked rubble for potential signs of life, but no one has been rescued since the first hours after the collapse.

“This is life and death,” Biden said during a briefing. “We can do it, just the simple act of everyone doing what needs to be done, makes a difference.”

“There’s gonna be a lot of pain and anxiety and suffering and even the need for psychological help in the days and months that follow," he said. "And so, we’re not going anywhere.”

Rescue work was halted after crews noticed several expansions in cracks they had been monitoring. They also observed 6 to 12 inches of movement in a large column hanging from the structure “that could fall and cause damage to support columns" in the underground parking garage, Miami-Dade Fire Rescue Chief Alan Cominsky said.

In addition, they noticed movement in the debris pile and slight movement in some concrete floor slabs “that could cause additional failure of the building,” he said.

Officials will work with structural engineers and other experts to “develop options” to continue rescue operations, Cominsky said.

Critical points around the site have been monitored with sensors since the rescue operation began, said Scott Nacheman, a structures specialist with the Federal Emergency Management Agency. He said there were alarming indications of movement Wednesday night at three locations.

“What was of specific concern was that over the last six days we had not seen that type of significant movement, or in some locations any movement in those elements of the structure,” Nacheman said Thursday during a briefing for family members.

Rescuers also use laser devices that can detect shifts of a few millimeters, Cominsky said.

“We are constantly monitoring the building,” he said.

Heavy equipment in the rubble pile caused vibrations, according to Nacheman. Rain has also been entering exposed parts of the building, saturating items and adding weight to the floors.

Covering parts of the structure to prevent further water damage or tearing down the building risks additional loss of life because those steps would require sending people back inside, Nacheman said. Demolition would also add debris on top of areas that have already been cleared of rubble.

Peter Milián is a cousin of Marcus Guara, who died along with his wife, Anaely Rodriguez, and their two children, 10-year-old Lucia Guara and 4-year-old Emma Guara. Milián said he understands why the rescue work had to be temporarily halted and is confident search efforts will continue.

“I mean, they’ve done everything they can. But we trust the people that are on the ground. And obviously, they’ve got to do what’s best for their people, right? Because it is a dangerous situation,” he said.

During a private meeting with family members, Biden drew on his own experiences with grief to try to comfort them. Biden lost his first wife and baby daughter in a car crash and decades later lost an adult son to brain cancer.

“I just wish there was something I could do to ease the pain,” he said in a video posted on Instagram by Jacqueline Patoka, a woman who was close to a couple and their daughter who are still missing.

Biden spoke of wanting to switch places with a lost or missing loved one. “The waiting, the waiting is unbearable,” he said.

Miami-Dade County Mayor Daniella Levine Cava said the search-and-rescue operation will continue as soon as it is safe to do so.

Gov. Ron DeSantis said state engineers, the fire department and county officials are exploring options on how to deal with the structural concerns.

“Obviously, we believe that continuing searching is very, very important,” DeSantis said, adding that the state will ”provide whatever resources they need" to allow the search to continue.

Cominsky confirmed Thursday that workers tried to rescue a woman shortly after the building collapsed when they heard a voice in the rubble.

“We were searching for a female voice ... we heard for several hours, and eventually we didn't hear her voice anymore,” he said.

Cominsky said they continued searching. “Unfortunately, we didn't have success on that,” he said.

The cause of the collapse is under investigation. A 2018 engineering report found that the building's ground-floor pool deck was resting on a concrete slab that had “major structural damage” and needed extensive repairs. The report also found “abundant cracking" of concrete columns, beams and walls in the parking garage.

Just two months before the building came down, the president of its board wrote a letter to residents saying that structural problems identified in the 2018 inspection had “gotten significantly worse” and that major repairs would cost at least $15.5 million. With bids for the work still pending, the building suddenly collapsed last Thursday.

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Associated Press writers Freida Frisaro in Fort Lauderdale and Mark Kennedy in New York contributed to this report.