Airport chief executive David Lanham said earlier this afternoon the incident related to the terminal carpark area.
The entrance to the airport had been blocked and some passengers had been secured inside the terminal, he said.
Other people wanting to enter the airport for flights or to pick up others were waiting on Airport Drive outside the terminal, he said.
"Police are on site and are in control of the scene. We're really being guided by them at the moment."
He said police were doing a really good job keeping everyone up to date.
"Everyone is comfortable and safe in the terminal."
Police were preparing to sweep through the carpark with bomb sweeping devices, he said.
"We've had a couple [flights] land and one has been diverted away. Nothing will be departing until the scene is deemed to be safe."
All flights were later cancelled.
A police spokeswoman said officers were responding to a report of a threat being made around 2.16pm.
"Police are working to establish the circumstances surrounding the threat and to speak with those involved."
Flights are expected to restart tomorrow morning.
- with RNZ
