A spokesperson for Transport NSW said a tree root wrapped around a private gas service was pulled out of the ground during excavations.

"The end cap of the gas service was dislodged as a result," a spokesperson said.

"The gas service was not directly connected to any structure.

"The area was made safe and there were no evacuations.

"Work was stopped and Jemena was called to re-cap the gas service."

12:40

It is understood the gas leak has now been isolated.

Fire and Rescue crews have left the scene.

The cause of the leak is still unknown.

12:10

A gas leak has been discovered at the Nowra Bridge works, causing twenty people to be evacuated.

At 11:38am on Thursday, July 2 Fire and Rescue NSW was alerted to a gas leak at the Nowra Bridge works off Scenic Drive.

Upon arrival crews found a gas main with a substantial rupture.

Shoalhaven and Berry Fire and Rescue crews isolated power and currently remain on scene.

The crews are waiting on attendance from the gas company to isolate the leak.

Some roads in the area are believed to have been closed off, take care if you are driving around the area.

More to come.