Police and the NZ Defence Force urge people setting up geocaches to put a little thought into the items they leave for other Geocachers to find, especially if it could be mistaken for an explosive device.

Geocaching is an internet-based treasure hunt using GPS co-ordinates, which began in the US in September 2000.

Geocaches are devices fitted with GPS, hidden in containers, the co-ordinates of which can be found online and the challenge is to find them.

Sometimes clues are hidden in objects left in plain sight, says a police spokesperson.

"A geocache clue was placed in what appeared to be an explosive device and left on a Nelson park bench on December 7, sparking a Police and NZDF response, which led to significant disruption including street closures.

"Police don't want to spoil people's fun, but we'd like them to avoid making geocaches that look suspicious - especially if they look like explosive devices.

"Please apply some common sense to where you put them and be aware that people will come looking for them and may be disrupting others, especially in urban areas."

Police say geocaches cannot be left on private property without permission of the landowner.

"The NZDF maintains a permanent response to any part of New Zealand, 24/7, 365 days a year to assess, remove, or destroy any potentially hazardous explosive items.

"If you do find any suspicious or potentially dangerous items please contact Police immediately and do not touch them.

"Further advice on dealing with suspicious or potentially dangerous items is available on the Police website."