Police, paramedics and firefighters were all called at 6.35pm to the Dobson Park Industrial Estate in Manchester Road and conducted a large scale evacuation.
As many as 30 emergency vehicles have been counted at the site.
Four fire engines from Greater Manchester Fire and Rescue Service attended, and three firefighters wearing breathing apparatus isolated the leak from inside of the industrial building and are working closely with onsite engineers to monitor and isolate further systems.
230 workers were evacuated from the building and assessed at the scene by paramedics. 10 people were taken to hospital as a precaution.
The incident was later scaled down to just two fire engines.
The air quality was also tested by monitoring systems and there is no cause for concern for the local area.
Officer in Charge, Craig Pinder said: “We are working closely with our partner agencies at this incident to ensure that the area is safe and that the leak has been isolated. We will continue to work with onsite engineers to monitor the building over the next hour.
“I would like to thank all those involved at this incident for their hard work.”