Parafield Airport in Adelaide has been shut down as tactical police search for a man seen on the runway in dark clothing before he fled into a drain.
Police were called to the airport on Kings Road about 3.25pm on Sunday, after reports that a man dressed in dark clothing was seen near the runways.
A manhunt is underway after Special Tasks and Rescue Group (STAR) group officers were called in to search the area.
Fire crews and the dog squad were called in to help with the search
The man has not yet been located.
It is understood that no flights were affected and no aircrafts were put in danger.
STAR forces entered the drain at around 5:30pm in an effort to find the man.
They were seen leaving the drain, but came back empty handed.
The airport was closed following the man being spotted.
Flights resumed around two hours later, with a plane arriving from Whyalla just after 4:45pm ACST.
SA Police are urging anyone who may have witnessed the incident to call Crime Stoppers on 1800 333 000.