The Glenn Miller Orchestra visited Devonport Naval Base earlier this month. A US navy vessel may be welcomed there late next year.

The New Zealand navy has issued an invitation to the United States to join in the navy's 75th birthday celebrations next year, potentially ending the 30-year freeze on military ship visits here.

However, sources said while an invitation had been issued, it was not yet clear that a ship would visit. It could be some other "asset" from the US Navy.

New Zealand's nuclear free policy, enacted in 1985, bans nuclear-powered and nuclear-armed ships from entering ports here. The law change saw New Zealand suspended from membership of the three-power Anzus alliance with the US and Australia.

While the law requires the prime minister to confirm, to his satisfaction, that any ships are not nuclear armed or powered, it has in practice always required the US to drop their "neither confirm nor deny policy".

The US has made it clear surface vessels are not nuclear armed, and it will be easy to ascertain from public records whether it is nuclear powered.

However in the past that has not removed the roadblock to the US sending a ship - the neither confirm nor deny issue - even though there have been suggestions a low-profile visit, such as by a coast guard vessel, could solve the impasse.

Labour deputy leader Annette King said she did not believe New Zealanders would accept the PM could decide to end that policy.

Foreign Affairs Minister Murray McCully on Friday said foreign military aircraft and vessels visit New Zealand on a regular basis.

"Our law requires the Prime Minister to make a determination that foreign military aircraft and vessels are not nuclear powered or carrying nuclear weapons before entering New Zealand.

He said the Ministry of Foreign Affairs and Trade advised the Prime Minister "to assist in his determination".

"The same legislation applies to all foreign visiting military aircraft and ships."

But McCully was not available for interview.

In a statement the navy confirmed next year's 75th commemorations in November would include an international naval review.

"It is common practice to invite a large number of navies to participate in such commemorative activities. Over 30 other nations have been invited to attend the review, including the US. This reflects the good bilateral relationship we have with the US," it said.

"The US is considering the invitation. We do not expect to receive decisions about how invitees will be represented until closer to the time."