Rescue crews searched for a missing construction worker after a section of a building scheduled for demolition collapsed June 18, officials said.

The accident occurred shortly after 11 a.m. EDT just inside Welsh Auditorium, a portion of the Grand Rapids Convention Center that was due for demolition as part of a $212-million renovation project.

”We know that there were two men working within an enclosed stairwell in Welsh Auditorium,’ said Annette Guilfoyle, spokeswoman for the city of Grand Rapids. ”One left to get tools and when he returned, there’d been a collapse within a stairwell. One worker is unaccounted for.’

Guilfoyle would not disclose the missing worker’s identity.

Fire Chief Mike Burton told radio station WOOD-AM a 20-by-20-ft. concrete slab fell from an unknown height as workers were preparing the building for demolition. The structure is attached to the Amway Grand Plaza Hotel by a second-floor skywalk, officials said.

Authorities said engineers were surveying the structure to determine how toproceed with rescue efforts. Crews used a special search camera obtained from a fire equipment exhibition at nearby DeVos Hall to assist rescue efforts.

”They had a small piece of conduit and fed the camera into the search site,’ Guilfoyle said.

Jon Nunn, executive director of The Grand Action, a private organization that helped put together the convention center development deal, said workers recently had begun asbestos abatement efforts in Welsh Auditorium.

The auditorium was to be demolished and replaced by a 40,000 sq. ft. (3,716 sq m) ballroom, part of an expansion and renovation project that when completed was expected to cover about 1 million sq. ft. (92,903 sq m), Nunn said.