Part of Fonterra's factory in the Waikato was momentarily shut down this morning after a chemical scare.
The Fire Service was called to Fonterra Hautapu at 3.20am after a high pressure air hose broke in a service tunnel.
Thirty-five firefighters and the hazardous material unit attended.
Shift manager Jaron Phillips said no gas was found. Crews would determine the damage.
A Fonterra spokeswoman said the eastern side of the plant was shut.
No-one was injured and staff were working with the fire crews to find out why it broke.
In August, there was a chemical spill at Fonterra's plant in Edendale, Southland.
About 5000 litres of nitric acid and a caustic alkali spilled from storage tanks into a containment area.
WorkSafe investigated after a milk silo collapse at the Southland plant weeks later.