About 180,000 chickens on a farm that reportedly supplies Tegel chicken died of suffocation on the weekend after a power cut.
The Ministry for Primary Industries director of compliance Gary Orr said a "large number" of chickens had died at the farm in Helensville, west Auckland.
"After being alerted to this issue today, and having spoken to the company involved, we have had it confirmed that there was an incident in the early hours of Saturday morning at a chicken farm in Helensville that resulted in the deaths of a large number of chickens due to a power failure and a subsequent generator issue," Orr said.
"Any such incident is extremely concerning to us and we are now investigating."