Uranium ore that is being shipped through New Zealand ports is an extremely low-risk material, Prime Minister John Key says.
The Green Party is complaining about the shipments and says they conflict with anti-nuclear policy, but the Government doesn't think so.
Shipments of Australian uranium ore, known as yellowcake, have been going through New Zealand ports for the last 20 years but were not revealed until this week. It goes to nuclear industries in Europe and the United States.
Until this year there was only one shipment a year, but because routes have changed there is now about one a week.
Mr Key said he had been surprised to find out about the shipments when he became prime minister.
He said he asked the obvious question -- were the shipments an environmental risk?
"The answer was that they are very, very, very low risk. It's not enriched uranium," he told reporters.
Mr Key said Australia asked for the ore to be trans-shipped, which would allow it to be taken off boats, but the Government rejected that.
He said the shipments did not make a mockery of New Zealand's nuclear-free position because it was not enriched uranium.
Environment Minister Nick Smith told Parliament it was important for people to keep the situation in perspective.
"Yellowcake has very low levels of radioactivity. If you stood right beside it for about a week, right by one of the drums, you'd get about a similar level of radiation as you would get naturally from the environment over about a year," he said.
It would have to be eaten to cause any harm, he said, and Australia had given assurances it would be used only for peaceful, non-military purposes.
Green Party co-leader Russel Norman said it was worrying that neither the present nor the previous government had seemed to be aware of the shipments.
"Clearly, bringing uranium through New Zealand on a regular basis goes against our nuclear-free policy," he said.