Seoul. Three people were killed and three others were injured Tuesday when a decades-old overpass undergoing demolition partially collapsed in the South Korean capital, fire officials said.

The accident occurred during a safety inspection after workers halted demolition work upon noticing that a part of the structure had slightly sunk. At the same time, concrete slabs were being cut, said Lee Jong-woon, an official at Seoul’s Seodaemun District Fire Station. The victims were crushed by debris and other wreckage after a section of a bridge deck suddenly collapsed, officials said.

Police and emergency officials sealed off traffic around the site, where twisted steel beams and shattered slabs of concrete hung precariously from the edge of the overpass.

Some debris also fell on a nearby railway, forcing the Korea Railroad Corp. to suspend some operations to Seoul Station.

Built in 1966, the overpass had been undergoing demolition since August last year over safety concerns.