Rescue efforts at the site of a partially collapsed Florida apartment building have been halted amid concern about the stability of the remaining structure after crews noticed widening cracks and up to a foot of movement in a large column.

The stoppage threatened to keep search teams off the rubble pile for an unknown period and to reduce hopes of finding anyone alive in the debris a week after the tower came down near Miami

The rescue operations were called off on the day President Joe Biden and first lady Jill Biden visited the devastated community.

The collapse of the 12-storey Champlain Towers South beachfront development killed at least 18 people and left 145 missing.

Hundreds of search-and-rescue personnel have painstakingly searched the rubble for potential signs of life, but no one has been rescued since the first hours after the collapse.

“This is life and death,” Mr 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 going to be a lot of pain and anxiety and suffering and even the need for psychological help in the days and months that follow. 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 6in to 12in 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, Mr 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 on 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,” he said during a briefing for family members.

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

During a private meeting with family members, Mr Biden drew on his own experiences with grief to try to comfort them. His first wife and baby daughter were killed in a car crash and decades later he 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.

Mr 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.

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.

Two months before the building came down, the president of its board wrote a letter to residents saying structural problems identified in the 2018 inspection had “gotten significantly worse” and that major repairs would cost at least 15.5 million dollars.