An outbreak of the highly pathogenic H7N6 virus in two sheds of the Hillgrove farm managed by Mainland Poultry initially led to the cull of about 80,000 hens.
Biosecurity NZ said over the weekend a third and fourth shed had tested positive, and the 80,000 chickens in the sheds would also be culled, bringing the total number of birds killed to 160,000.
"The farm remains under strict biosecurity lockdown," the Ministry for Primary Industries’ (MPI) chief veterinary officer, Dr Mary van Andel said.
"There have been no reports of sick poultry elsewhere in the country. There remains no risk to eggs and chicken supply in New Zealand given the size of the national flock, nor any issues for food safety and human health."
Biosecurity New Zealand deputy director-general Stuart Anderson said MPI officials continued to work to resume trade of chicken products after a halt due to the outbreak.
"We’re in close contact with the relevant trade partners and working with them to resume trade, with positive progress being made.
"New Zealand has reached agreement with Australia to continue the export of some poultry products, including chicken meat, dried pet food and dog rolls that meet avian influenza heat treatment requirements," he said.
"Australia, like New Zealand, is taking a risk-based approach."
A second farm south of Dunedin was also under investigation after some chickens were found sick and dying, but test results were negative for bird flu.
Mr Anderson said MPI believed the issues on that farm were caused by an existing New Zealand disease among the birds and it continued to work with the farm to identify what was needed and provide support.
MPI earlier this week said it was confident it had the resources to handle a wider bird flu outbreak.
All poultry exports were on hold until the country was free of the disease.
The version of the virus found in New Zealand is different from the H5N1 strain which has infected people overseas.
