Passengers arriving into Auckland International Airport's baggage hall are being evacuated on Monday afternoon.
Auckland Airport told Newshub a sprinkler was knocked and set off, triggering the alarm. Fire and Emergency are attending.
It's the second incident to strike Auckland Airport on Monday after flights were temporarily suspended due to a bomb threat.
A caller to 111 just after 6:30am on Monday claimed there was a bomb in a building at a location near the airport.
Auckland Airport said on its Twitter account flights were temporarily stopped at the request of the police.
Flight tracking websites showed landings resumed just before 9:15am. Planes were forced to fly in circles awaiting approval to land.
Insp Joe Hunter said police found nothing suspicious.
"There will be a criminal investigation... to try and find the person responsible," he said.