Television footage showed emergency workers conducting a search-and-rescue operation as a long segment of the structure lay collapsed on the street below, near a railway crossing in central Seoul.
Workers detected signs of instability in the structure overnight and suspended the demolition early on Tuesday for a safety inspection, a Seoul city official said.
The section collapsed on Tuesday afternoon while safety inspectors were inside the support structure, the official said.
All the people killed and injured were senior city public works officials and a private sector expert conducting the inspection, a fire official said.
The overpass, built in 1966, was being demolished due to safety defects in the ageing structure, the city said.
(Reporting by Jack KimEditing by Ed Davies)

Search and rescue operations are under way at the site of an overpass collapse in western Seoul, South Korea, 26 May 2026. The aging overpass was being dismantled at the time of the collapse. EPA/YONHAP SOUTH KOREA OUT