First responders are still searching for two missing workers in the debris of a collapsed library construction site in Gwangju.

Gwangju's fire department said Friday that it had conducted an overnight search but has yet to locate the missing workers.

Authorities said thermal imaging cameras and rescue dogs are being utilized in the search. Heavy equipment, including large cranes, has also been deployed to stabilize the collapsed structure and prevent further collapse.

However, progress has been slow due to massive steel bars tangled throughout the wreckage, and concrete poured on Thursday, which is beginning to harden in the cold weather.

The collapse occurred around 2 p.m. Thursday as workers poured concrete on the two‑story structure’s rooftop. Two workers have been confirmed dead, and two remain unaccounted for.