Chemical giant Orica is close to finishing the clean up of another ammonia spill at its Newcastle site.
It is the latest in a series of toxic leaks at Orica's Kooragang Island site which in 2011 resulted in the shut down of the ammonium nitrate plant.
At around 4:00am (AEST) Orica workers discovered a leaking pipe containing about 100 kilograms of liquid ammonia.
Fire and Rescue New South Wales' Greg Symonds says they were called about three hours later.
He is not sure how much of the chemical was lost but says the danger is contained.
"With the monitoring, from a 30-metre distance, we have a zero reading for any ammonia gas," he said.
"We've also taken readings down wind as well for 100, 150 metres and again got zero readings.
"So it is contained locally and we've notified WorkCover and EPA (Environment Protection Authority) to attend."
He says residents in surrounding suburbs including Stockton will not be notified of the leak because nothing has escaped off-site.
Orica's Kooragang Island general manager Greg Holmes says the incident is very minor.
"None of our instruments could pick up the amount that's leaking because it's so small," he said.
He says the faulty pipe should be repaired by later this afternoon.