A man is in custody after triggering an emergency evacuation of Brisbane's International Airport, the grounding of planes, and suspension of trains because he was carrying a knife and, authorities feared, an "explosive device".

In what police believe was a "domestic violence-related situation" not a terrorism-related incident, Superintendent Tony Fleming said officers were concerned the man had a "dangerous device" in his luggage but it turned out not to be the case.

"Certainly the presentation of the device and his demeanour certainly gave us cause for concern,'' he said.

The international terminal was locked down and searched as well as the man's car which was parked at the airport. A second car at Surfers Paradise was also searched.