Prime Minister John Key says there is enough "free information" for the Ministry of Foreign Affairs (MFAT) to know which US ships are nuclear powered or armed and would break New Zealand law if they entered Kiwi waters.
When questioned whether he had a more relaxed attitude to New Zealand's nuclear-free stance than other prime ministers, Mr Key said he was "very cognisant" of his responsibilities to meet the law.
"The Americans have for a long time had a neither confirm nor deny policy, but they've also had enough open source intelligence about which particular ships are either nuclear-armed or carry nuclear weapons," he said at his post-cabinet press conference today.
"Foreign Affairs can make an assessment in its own right whether something is nuclear-powered or capable.
"Whether they ask them or do it through open source intelligence I don't know, a lot of ships aren't nuclear-armed or nuclear-powered," he said, when asked if MFAT would rely on Google for information on US ships.
The US been invited to send a ship to New Zealand for the Navy's 75th anniversary later this year but hasn't yet decided whether it will.
China has also been invited and it's "highly likely" a Chinese ship will come, Mr Key said.
The anti-nuclear legislation affects any navy ship that comes to New Zealand, and in 1985 a visit by the USS Buchanan was blocked because the US wouldn't confirm or deny its nuclear capabilities.
Mr Key has to sign a waiver for any navy ship that comes here.
"Our anti-nuclear legislation isn't country specific, any ships that comes has to meet our law," he said.
China and the US both have nuclear armed submarines.