GANGNEUNG, (Yonhap) -- All four workers who had been trapped under a collapsed reservoir construction site here were found dead early Friday, rescuers said.

   The scaffolding at the site in the city of Gangneung, 237 kilometers east of Seoul, collapsed at around 4:30 p.m. Thursday while four workers were doing concrete work to build a waterway for a reservoir to prevent flooding.

   Rescuers have retrieved the bodies of all the men from a giant hole that was as deep as five meters during an overnight search, officials said. Three of the victims were identified as in their 40s and one in his 60s.

   Three other workers who were near the site of the collapse were sent to a nearby hospital for treatment.

   Police said they will investigate the exact cause of the incident and whether the construction company had violated safety regulations.