A spokesman for NSW Police told news.com.au officers were called to the site on Coward Street at Mascot about 11am today.
A man with suffering stab wounds has been transported to hospital, according to police. A spokesman for NSW Ambulance told news.com.au the man, believed to be 27, was in a serious condition, after he was stabbed multiple times.
Police remain on the scene, interviewing witnesses.
The incident comes after two recent knife attacks at construction sites.
Vladimir Kondakov stabbed a father and son at a construction site earlier this month in St Peters, in inner west Sydney.
The father, 76, Albert Metledge, 76, was killed by the attack while his son, Antony Metledge, 33, was hospitalised in a critical condition.
Kondakov fled the scene and was later found dead in a park.