A man is in hospital after he was impaled on a steel bar for up to an hour following a fall at a construction site on the NSW central coast. 

Emergency services were called to the site in Gosford just before 3pm on Tuesday, where the 35-year-old man is believed to have tripped and fell from the eighth floor to the floor below, landing on the bar.

The man was impaled through his thigh, a NSW Ambulance spokesman told AAP.

Emergency services treated the man, including sedation, before fire crews were able to cut the bar and free him, CareFlight said.

He was transported to Gosford Hospital in a serious but stable condition.