Three workers were evacuated from Whanganui's Affco Imlay plant Thursday night after being exposed to a "significant ammonia leak".
Whanganui Fire and Emergency assistant area manager Dave Utumatu was called to the scene on Bryce St about 8.20pm Thursday night.
"We had a significant ammonia leak at Affco and we responded to the second alarm with five fire crews on scene."
St John Ambulance spokeswoman Jess Miller said one worker was taken to Whanganui Hospital with moderate injuries and two others were treated for minor injuries at the scene after the evacuation.
A Whanganui Hospital duty nurse said the injured worker was treated and discharged overnight.