TOKYO -- Three workers were killed, and one remains missing after scaffolding collapsed during crane dismantling operations at a steel plant in Kawasaki City, near Tokyo, local media reported.

According to public broadcaster NHK, the accident occurred at around 4:30 pm local time on Monday at a portside steelmaking complex in Kawasaki, Kanagawa Prefecture. A scaffold standing approximately 40 meters high collapsed, causing five workers to fall.

Four were rescued and taken to the hospital, but three were later pronounced dead. The fifth worker remains missing, who is believed to have fallen into the sea.

At the time of the accident, dismantling work was underway at the site on a crane used for loading and unloading cargo from ships. A cylindrical counterweight of roughly 500 tonnes, which had been attached to the crane for stability, came loose and fell. The impact is believed to have caused the surrounding scaffolding to collapse, the report said.

Police are investigating the detailed circumstances of the accident, including whether adequate safety protocols were in place during the demolition work. Rescue is also underway to locate the missing worker as quickly as possible.