SEOUL -- Two workers were killed and two others remained missing after a steel structure collapsed at a library construction site in South Korea's Gwangju on Thursday, according to Yonhap news agency.

Search operations continued for the missing workers believed to be trapped under the structure.

The collapse occurred around 1:58 pm local time (0458 GMT) in Gwangju, some 270 km south of the capital Seoul. Firefighting officials said the structure appeared to have collapsed while ready-mixed concrete was being poured, the report said.