The man was on scaffolding stripping materials from the exterior of a lift shaft when he plummeted to the ground just after 8 a.m. (AEDT) Saturday, AAP reported authorities as saying.
He was taken to St. George Hospital in a serious condition.
WorkCover, dedicated to promote productive, healthy and safe workplaces for workers and employers, has launched an investigation at the building site in Willarong Road.
"Working from heights can be dangerous and, as this incident highlights, a fall can result in serious injury or death," WorkCover NSW manager John Watson said in a statement.