Police were patrolling in Wollongong just after midnight when they noticed the 20-year-old hanging on the fence at a Flinders St car yard.

The fence pole had entered the man's leg behind his calf and exited near his knee, Acting Inspector Paul Allman said.

Police officers supported the man's weight until a NSW Fire Brigade rescue team was able to cut off the pole and free the man.

The man was left hanging on the fence for up to 40 minutes before he was taken to Wollongong Hospital for treatment.

Insp Allman said the man had been walking home from a night out in Wollongong when he decided he needed to relieve himself.

The man had jumped the main fence, but landed on a secondary fence not far behind it.

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 until he was put in the ambulance with a cut off part of the fence still in his leg," the spokesman said.

Last night's accident was the second impaling in a week.

On Sunday a Nowra man was impaled by a garden stake in a motorcycle accident - and is believed to have been robbed and assaulted while suffering his life-threatening injuries.

The 39-year-old allegedly stole a bike and was riding it along Adelaide St, Greenwell Point, when he lost control.

A timber metre-long garden stake was driven through his right armpit and out his back. Paramedics arrived to find the man conscious and the stake already pulled from his body.

Nowra police confirmed there was no motorcycle at the scene when authorities arrived.

A source said the owner of the bike had caught up with the rider, pulled out the stake and punched him on the nose before taking his wallet and reclaiming the motorcycle.

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