Factories and businesses along Old Punt Road, Tomago were evacuated following a toxic chemical spill, which has now been contained.
The chemical, methyl ethyl ketone, also known as Butanone, was spilt from a 1000 litre plastic container at CQMS Razer in Laverick Ave at 2.06 pm.
It is estimated 100 litres of the chemical escaped from the drum when it split after falling off a forklift.
The chemical, commonly used as an industrial solvent, has an ignition point of -6 degrees.
It did not get into any waterways.
A 300 metre exclusion zone was set up around the site and about 75 people were evacuated.
A NSW Fire and Rescue spokesman said crews had islotated all potential ignition points and were focusing on mopping-up the spill.
Motorists can expect traffic delays in the area due to the closure of Old Punt Road.