Avian influenza was found at a second NSW poultry farm over the weekend, however the property is inside a biosecurity zone that was set up in the Hawkesbury district after an initial detection on Wednesday.
The flu has also been picked up at seven farms in Victoria, but all involve a different strain from the NSW variant - which authorities believe came from wild birds.
More than 320,000 animals will be destroyed across the two NSW farms in a bid to curb the outbreak, on top of the one million birds to be killed in Victoria.
Australian Eggs boss Rowan McMonnies acknowledged some supply chain disruption would be experienced as a result of the mass culls.
But he said consumers would at worst see a minor inconvenience when trying to purchase, adding "if you want eggs, you will get them".
"You may not be able to get eggs every time you usually do, (but) there's still going to be a lot of eggs available over the winter," he told ABC radio on Monday.
"We really are cautioning against any form of panic ... there's no food safety issue in relation to these incidents, eggs, chicken meat, duck meat are all safe to eat and consumers need have no concern in that regard."
Coles has placed purchase limits on eggs following the outbreaks, but the other major supermarket chains are yet to follow suit.
Experts say the disease does not pose a risk to human health, but Mr McMonnies said culling birds was the correct course of action due to the "terrible" welfare impact it has on them.
"The notion we could let it rip and let this go out of control is not right at all ... these things need to be eradicated and stamped out, because they're very damaging," he said.
Four NSW farms have been quarantined under the state's emergency biosecurity incident plan, with movement controls in place in the Hawkesbury area northwest of Sydney.
Premier Chris Minns said it was unfortunate that bird flu had been found at a second property, but it was important to note it was still within the original contagion area.
Federal Agriculture Minister Murray Watt also noted the disease had not spread to further farms in Victoria since the early discoveries.
"It is pleasing to see in Victoria, the number of farms infected has remained at seven for quite a few days now," he said.
"There is absolutely no risk of egg supply shortages, of course there are particular shops in particular places that might be having a little bit of trouble getting them from their usual supply chains, but there's no need whatsoever for shoppers to be panicking about this."
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