Gwangju, Dec 11 : A steel structure collapsed at a library construction site in the southwestern city of South Korea's Gwangju on Thursday, killing two workers and trapping two others, authorities said.

The accident was reported at 1:58 pm, prompting firefighters to respond to the scene where they rescued a 47-year-old worker, who was taken to a hospital in cardiac arrest but later pronounced dead.

Firefighters spotted the second victim, who remained unresponsive, earlier in the day, before finally rescuing him at 8:13 pm, according to officials, Yonhap News Agency reported.

He was pronounced dead on site, with officials working to figure out the identity of the victim.

Two others are still unaccounted for, officials said, adding they plan to continue search operations overnight.

The four victims were identified as technicians affiliated with a subcontractor, with all of them being Korean nationals.

Firefighting officials said the structure appeared to have collapsed while ready-mixed concrete was being poured.

A construction site official told Yonhap News Agency the rooftop of the second floor appeared to have collapsed down to the first floor, with no supports installed in between.

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

The 51.6 billion-won (USD 35 million) project was being built to cover a total floor area of 11,286 square meters across two stories above ground and two floors in the basement.

Meanwhile, South Korean President President Lee Jae Myung ordered authorities to make all-out efforts to rescue workers trapped in the rubble of a collapsed library construction site in the southwestern city of Gwangju.

Lee gave the instruction during a policy briefing by the labour ministry in the administrative city of Sejong, after a steel structure at the construction site collapsed at around 2 p.m., killing one worker and trapping three others.

Lee called on the relevant ministries to "mobilize all available personnel and equipment" to rescue the trapped workers.

/IANS