A cache of more than 200 firearms and ammunition has been discovered buried in an old cesspit in the Auckland suburb of Glen Innes.
The rifles and shotguns, including pump-action guns, were found at a property now occupied by Montana Wines' head office.
Contractors were excavating the sitein preparation for the building of an office block.
The site supervisor immediately notified police, who called in a military firearms expert. The weapons were then removed from the site.
It was originally thought the cache had been dumped by the Army, but this has been ruled out because the weapons are not of military origin.
Montana bought the property, which included a house that was pulled down last week, about six months ago.
Police believe the firearms have been buried for at least 10 years.
Detective Senior Sergeant Andrew Lovelock, from Auckland Central, said that although ammunition was discovered, the risk of an explosion was small.
The firearms and ammunition were corroded and probably not in working order, and the site was in a contained area.
Mr Lovelock said police were making inquiries to find out the origin of the firearms.
"They may originate from a crime, such as a burglary of a gun collector or sports shop," he said.
It is believed all the firearms have been recovered, but the rest of the site will be searched today.
Mr Lovelock said the firearms expert would identify the type of weapons and, hopefully, how long they had been buried.
Montana Wines managing director Peter Hubscher said the company was concerned about employee safety and was taking advice from police and the firearms expert.
Company communications manager Zirk van den Berg said a building next to the site was evacuated on the advice of Montana's health and safety officer.
