The collapse was reported at about 2:32 p.m. in Migeun-dong, Seodaemun district. A section of bridge deck fell onto the work zone, crushing a demolition vehicle beneath concrete and twisted steel. Fire officials said the victims were trapped by debris and wreckage. Six other workers managed to evacuate without injury.
The three men who died included two in their sixties and one in his fifties. The younger man was found trapped beneath a vehicle, taken to hospital in cardiac arrest and later pronounced dead. The three injured workers, in their thirties, forties and fifties, sustained injuries to the waist, head and ribs.
Warning signs had appeared many hours earlier. Seoul officials said crews were cutting concrete slabs between 1:30 a.m. and 2:30 a.m., the restricted overnight window available because the overpass crossed active railway lines. A slab sank by 2.9 centimetres, prompting workers to halt construction. Inspectors returned at 2 p.m. Officials believed a girder supporting the bridge deck broke near its centre during that inspection, possibly triggering the collapse, but the exact cause remained under investigation.
The overpass was built in 1966 and had received a Grade D safety rating, indicating serious concerns. Seoul began dismantling it in August 2025. The project was therefore intended to remove an ageing structure already considered unsafe, making the fatal failure during a precautionary pause a central question for investigators.
Debris also fell onto the railway below. Korea Railroad Corporation suspended operations between Seoul Station and Sinchon, affecting the Gyeongui Line and nearby services. Police and emergency teams sealed streets around the site because broken slabs and beams remained suspended at the damaged edge.
President Lee Jae Myung ordered agencies to provide treatment for the injured, investigate the cause thoroughly and develop measures to prevent a recurrence. Prime Minister Kim Min-seok directed the Interior Ministry and National Fire Agency to mobilise personnel and equipment and identify hospitals able to receive casualties quickly.
The accident also interrupted campaigning before Seoul's June 3 mayoral election. Candidates Chong Won-o and Oh Se-hoon both suspended campaign activity, saying rescue and recovery took priority. Their decisions reflected the public significance of a failure involving a prominent piece of city infrastructure. Investigators now faced a precise sequence to reconstruct: overnight cutting, measurable movement, a work stoppage, and the apparent failure of a supporting girder while the abnormality was being examined.
