New Zealand will not lift a decades-long ban on nuclear-powered vessels entering its waters in the wake of key ally Australia's decision to develop a nuclear submarine fleet, Prime Minister Jacinda Ardern said Thursday.

Ardern said her Australian counterpart Scott Morrison had briefed her on Canberra's plan to develop nuclear-powered submarines with the help of the United States and Britain.

New Zealand's Prime Minister Jacinda Ardern says Australian nuclear subs will be banned from New Zealand waters
New Zealand's Prime Minister Jacinda Ardern says Australian nuclear subs will be banned from New Zealand waters POOL / Mark Mitchell

She described the deal as "primarily around technology and defence hardware", playing down implications for the so-called "Five Eyes" partnership of the United States, Britain, Australia, Canada and New Zealand.

"This arrangement in no way changes our security and intelligence ties with these three countries, as well as Canada," the New Zealand leader said in a statement.

"We have an independent foreign policy," says Prime Minister Jacinda Ardern, after confirming that New Zealand will not lift a ban on nuclear-powered vessels entering its waters in the wake of Australia's decision to develop a nuclear submarine fleet
"We have an independent foreign policy," says Prime Minister Jacinda Ardern, after confirming that New Zealand will not lift a ban on nuclear-powered vessels entering its waters in the wake of Australia's decision to develop a nuclear submarine fleet NZ Ministry of Health

But she also said New Zealand would maintain a ban on nuclear-powered vessels that dates back to 1985, meaning Wellington will not allow the prized naval asset being developed by Australia into its waters.

"New Zealand's position in relation to the prohibition of nuclear-powered vessels in our waters remains unchanged," Ardern said.

The ban was introduced in the wake of French nuclear testing in the Pacific and led to the US navy banning its warships from entering New Zealand ports for more than 30 years.

Official US policy is to neither confirm nor deny whether its vessels are nuclear-capable.