The bomb squad was called to the international mail centre at Auckland Airport after a "suspicious item" was found on Wednesday.
The NZ Post International Mail Centre was evacuated and shut down due to the incident.
The event occurred after an item was discovered in an X-ray machine and a manual sprinkler system was activated.
"Police are currently attending an incident at New Zealand Post at Auckland Airport where a suspicious item has been identified by an X-ray machine," a police spokesperson told Newshub.
"The building has been evacuated as a precaution until the scene can be cleared by the Defence Force as per standard protocol."
The bomb threat was later given an all-clear.