SURFSIDE, Fla. (AP) — Rescue efforts at the site of a partially collapsed Florida condominium building were halted Thursday out of concern about the stability of the remaining structure after crews noticed widening cracks and up to a foot of movement in a large column, officials said.

The stoppage that began shortly after 2 a.m. threatened to keep search teams off the rubble pile for an unknown period and dim hopes for finding anyone alive in the debris a week after the tower came down.

The rescue operations were called off 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.”

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.