Rescue officials have suspended the search for missing workers trapped under the debris of a collapsed boiler tower at a thermal power plant in the southeastern city of Ulsan due to safety risks.

According to fire authorities, a situation assessment meeting held at 7 a.m. Sunday concluded that it was too dangerous to continue search operations inside the structure.

Rescue engineers cited overnight rain and wind, as well as work done on the structure before it collapsed to prepare it for demolition, as risk factors that might cause the wreckage to collapse further.

Instead, fire officials said they began using drones at 8:10 a.m. Sunday to search for the missing workers and the drone operations will continue even as pre-demolition work proceeds on two adjacent boiler towers.

A tilt sensor alarm was triggered at the collapsed tower around 5:25 p.m. Saturday, prompting the immediate evacuation of all rescue personnel from the site.

Of the seven people who were initially trapped underneath the collapsed structure, three have been confirmed dead, two are presumed dead, and two remain missing.