Work at the site of the condo building collapse in Surfside, Florida, was halted early Thursday due to concerns about the part of the structure that is still standing, officials announced at a press conference. Operations halted shortly after 2 a.m.

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

The pause was prompted in part by 6-12 inches of movement in a large column hanging from the structure that could fall and cause damage to support columns, Miami-Dade Fire Rescue Chief Alan Cominsky said. There was also some movement in concrete floor slabs in the building’s south side, which could cause additional building failure.

Engineers and experts will now work to come up with options to continue rescue operations, Cominsky said.

The development comes as President Joe Biden and first lady Jill Biden are visiting Surfside. They were scheduled to receive a command briefing from the governor and other officials before meeting with families impacted by the collapse. Mr. Biden will later deliver remarks in Miami.

Levine Cava said the president’s visit will have no impact on what happens at the site.

Eighteen people are confirmed dead in the tragedy and more than 140 are unaccounted for.