Police cordoned off several blocks of Dunedin's inner-city wharf area after Customs officers spotted what appeared to be grenades and mortars while x-raying the container.
The police were later stood down when none of the cargo was found to be live.
Inside the container, police and Customs staff found, among other items, boxes of dummy .50 calibre heavy machinegun rounds and decommissioned grenades, mortar bombs and rifle grenades.
Explosive disposal experts from Christchurch declared the container safe last night.
NZ Customs Service spokesman Rowan McArthur said the weapons did not work, but did not appear to be imitation.
He would not elaborate on the case, except to say it was not just the weapons Customs were interested in, and there were "irregularities" with the entire shipment.
That included looking at who brought the items in, where and what they were destined for and if the importer had complied with all import declarations.
He could not expand because the investigation might result in court action, he said.
When asked, Mr McArthur said there were no guarantees items similar to those found in the Dunedin container did not occasionally slip into the country.
The same problem was faced by Customs operations the world over.
"I think you would find anywhere around the world, in any category of contraband, no-one would guarantee they are getting everything."
A spokesman from an army surplus supply store in Christchurch said it was usually collectors or people who re-enacted battles who were interested in replica or imitation weapons and dummy rounds.
People who want to import real or replica weapons need a permit from the NZ Police, and to declare the items to Customs.
