The 19-year-old engineering student had been walking home from a night on the town when he jumped a fence in Flinders St, to relieve himself, just before midnight.

After clearing the main fence, he landed on a secondary, ornamental steel fence not far behind.

The pointed, 60mm fence pole entered his right leg behind the thigh and exited below the knee.

The Fairy Meadow man was left hanging on the fence of the Avis Rent-A-Car yard until police noticed him just after midnight during a patrol.

Acting Inspector Paul Allman said police officers supported the man's weight until a NSW Fire Brigades rescue team arrived and cut out a three-pronged section of the fence to free him.

He was transported to Wollongong Hospital with the fence still embedded in his leg.

A NSW Ambulance spokesman said the man was conscious throughout the ordeal.

"The estimated time that he was in that situation was about 30-40 minutes," he said.

The post is believed to have passed through the leg without causing any major damage or arterial bleeds.

It was at first expected removal of the post would require a simple procedure with the aid of a local anaesthetic.

Soon after being assessed, however, the 19-year-old, who turns 20 on August 25, was transferred to St George Hospital.

Friends said the man, who is specialising in nanotechnology at the university, was a friendly, social person and "a nice guy".

"All of his mates are pretty concerned for him and they are all wishing him the best of luck in a speedy recovery," a friend said.

The 19-year-old was last night listed in a stable condition.