The situation has been contained after a major ammonia leak at the AFFCO processing plant on State Highway 1 in Moerewa, a fire services spokesperson says.
Fire services communications shift manager Megan Ruru says there were initial reports of staff being trapped inside, however everybody has since evacuated.
Fire services have now left the scene after emergency contamination procedures, and responsibility has been handed over to the building owner.
The amount of ammonia is now at acceptable levels, and the fire service has not been advised of any injuries.
Ammonia is a strong smelling colourless gas, often used for cleaning. It can be extremely dangerous if inhaled, irritating the skin, eyes, nose, throat and lungs.
Founder of the NZ Ammonia Safety Association Padraic Durham says it's "absolutely lucky" no-one was seriously injured.
"As an industry we are actively trying to educate businesses to ensure their engineering controls are as safe as possible," he says.
AFFCO Moerewa processes calves from slaughter through to further processing, according to the company's website.
It is the biggest employer in the region.
Newshub.
