Workers at the Affco Rangiuru plant near Te Puke had to be evacuated after an ammonia leak.
Te Puke volunteer fire brigade chief officer Glenn Williams told the Bay of Plenty Times the leak was "isolated by contractors" and firefighters ventilated the room contaminated by ammonia.
An Affco worker, who did not want to be named, said the plant was evacuated about 12.45pm on Thursday after alarms sounded.
"We all went out thinking it was just a fire drill, they didn't tell us what the problem was."
After spending 30 minutes outside the plant, workers were sent back inside "for a few minutes" to finish off "a few jobs", then sent on a 15-minute smoko break.