Five people remain trapped, but rescue efforts are hampered by unstable rubble and asbestos.
A 60-metre (196-foot) tower collapsed during demolition work at a decommissioned thermal power plant in the South Korean city of Ulsan, killing three people and leaving at least two others presumed dead, officials said on Friday.
Five people remain trapped under the rubble, including two whom officials have yet to locate.
Nine people were working at the site when the boiler tower collapsed on Thursday afternoon.
