(NewsNation) — Emergency crews are working to stabilize a Manhattan high-rise where two support columns buckled Tuesday, causing nine buildings to be evacuated, including a school with roughly 400 students. Repairs are underway.

Officials said the building is still moving, through it’s not considered at imminent risk of collapse.

The building, a 1970s-era former office tower for Pfizer’s global headquarters, was being converted into luxury apartments. Records show the building has been cited several times for safety violations over the past year.

The New York City Fire Department got reports of bricks falling from the building Tuesday, and crews found columns on the building’s 21st floor had buckled, causing the floors above to sag and crack. FDNY Commissioner Lillian Bonsignore said an assessment determined the building was unstable, and crews set up a collapse zone around it. No injuries were reported, and all workers inside were accounted for.

Engineer: Columns were carrying too much weight

Structural engineer Brian A. Falconer, managing principal at Severud Associates Consulting Engineers in New York, said a column buckles when it’s carrying more weight than it can handle.

“It’s unusual for this to happen in a high-rise, but anytime a column buckles, it’s because it took on more load than it could carry. So, basically, the columns that were there weren’t strong enough to carry the load that was applied to them,” he said.

He said buildings are typically built so that when one column fails, the weight shifts to nearby columns, which is likely why the building didn’t collapse.

Changes to building structure during conversion may have caused failure

Falconer said swapping offices for apartments on a one-to-one basis shouldn’t overload a building, since residential floors typically carry lighter loads than office floors. But adding extra floors or otherwise changing a building’s structure can create strain that leads to failures — though he noted it’s common for engineers to plan and reinforce buildings for that kind of change.

“It’s actually done pretty frequently in New York,” he said.

How the building could be repaired

To repair the building, Falconer said the damaged columns may be replaced or reinforced, or support could be added elsewhere in the building in the form of “transfer girders,” which are beams that redirect weight away from the damaged section.

He said the damaged floors above will either need to be reconnected or rebuilt entirely.

Falconer said the engineering fix itself is fairly straightforward and can be done to meet New York City’s strict building codes, but will take time.

“I think that it’s going to be able to be designed to be safe, to restore it to what it was and better,” he said.