Police are to forensically test a sinister note claiming a bomb was on board a plane from Wellington to Dunedin which led to an evacuation of Dunedin Airport.
They will also study CCTV footage to try and find the person responsible, who could face charges under the Civil Aviation Act and the Crimes Act.
Acting Wellington Area Commander Detective Inspector Stephen Vaughan said the note was found in the women's toilets near Gate 14 at Wellington Airport about 10 minutes after Flight 459 departed the Capital around 7pm last night.
''I'd prefer not to say the actual words on the note... but it referred to a bomb on that flight. What was written on that note led us to believe it related specifically to that flight.''
Police conducted initial inquiries and searched the toilets last night, he said.
''Now the note will be subject to forensic testing and CCTV footage of the airport and its environs will also be conducted.''
A police search of the aircraft involved in the scare had been completed and nothing of interest was found. But that provides cold comfort to the police.
''Certainly notes being left... saying bombs have been left on flights is unusual for Wellington Airport. We are highly concerned about it [and] we treat it very, very seriously.
''With the heightened security environment it is a note we certainly don't want to be seen in our airports.''
The flight was already en-route to Dunedin when the note was found, Dunedin International Airport CEO John McCall said.
The plane arrived at 8.15pm and the airport was evacuated and a cordon set up by 8.30pm.
Air New Zealand believed the bomb threat was a hoax, however standard procedure was followed, spokeswoman Tracy Smeaton said.
"No one knows why people do these things because at the end of the day there's no gain and it just causes a lot of disruption and pain to a lot of people," McCall said.
"It not only disrupts people's travel plans but there are also considerable economic impacts too."
The airport didn't reopen until 10.30pm, two hours after everyone was evacuated, and some people ended up having to change their travel plans, McCall said.
Dunedin police senior sergeant Steve Aitken said last night that all passengers had been safely taken off the plane.
"The plane is being removed to a secure location where it'll be searched, and depending on whether we find anything, that will determine what happens next," he said last night.
McCall said this morning that there was some confusion about whether it was a specific or non-specific threat.
The result of a police search of the plane when it arrived indicated it was a non-specific threat, McCall said.
"If it was a specific threat they would have sent bomb experts in," he said, "It seems it was handled differently at the airport to what it was on the aircraft."
Specific and non-specific refer to how much information was known about the threat, McCall said.
The airport treated it as a specific threat and would not have ordered an evacuation if it was believed to be a non-specific threat.
It was understood the flight was NZ459, which was carrying passengers from Auckland and Wellington.
St John South Island region communications and promotions coordinator Alena Lynch said four ambulances had been on standby in Dunedin.
Wellington International Airport spokeswoman Kat Lintott said no flights had been affected by the incident.