A Fire and Emergency New Zealand spokesman said emergency crews had been on site since 2pm today securing the site.
He said two bulk containers of chemicals have come into contact with each other creating a chemical reaction that has released dangerous gas on site.
The spokesman said specialist crew and equipment from Timaru was being used to help dilute the chemical.
"It's not a spill, but we're going to use the equipment to control the run off from the dilution so there's equipment to set up a bund."
He said there had been no reports of injuries.
There was no risk of gas escaping and harming people given how far away residential properties are from the site, which is well north of the town.
Information about what the two chemicals are was not unavailable.
Lean Meats Oamaru could not be reached for comment.
