Gwangju: Rescue authorities were racing to find two trapped workers under a pile of debris at a collapsed library construction site as search efforts entered the second day, officials said Friday. Search efforts were ongoing to locate the missing workers believed to be trapped under twisted steel and concrete debris, after the structure collapsed at 1:58 p.m. Thursday in Gwangju, about 300 kilometers south of Seoul.

According to Yonhap News Agency, four workers were initially trapped at the site, with firefighters recovering two of them - one was pronounced dead at the scene, and the other later at the hospital. Authorities suspect the collapse began as workers poured concrete onto the two-story structure's rooftop, with the ground floors falling to the underground level.

Officials have mobilized thermal-imaging cameras to locate the workers, while taking measures to stabilize the site in consideration of the possibility of further collapse. Rescue officials have slowly advanced to the underground level, where the workers are presumed to be located, cutting entangled rebar that have hampered the operation.

Search efforts are also facing difficulties as the concrete mixture has begun to harden with the rubble, prompting officials to shovel them out and pour water to dilute them. "While they haven't all hardened, we need to dig as much as we can before they completely harden," a rescue official said. "It will ultimately be a race against time."

The library under construction was being built by the Gwangju metropolitan government on the site of a former waste incineration plant.