Queenstown Airport operations and safety general manager Mike Clay said all kitchen utensils used in the international lounge were recorded and accounted for regularly.
The utensil in question was a small paring knife, between 6.5cm and 7cm long.
Regulations dictated any knife longer than 6cm which went missing had to be reported, he said.
"Safety and security is our highest priority, so when one item could not be accounted for, we took the step of rescreening all international passengers and this led to some delays.
"We will always put the safety and security of our passengers and staff first."
Some passengers were asked to go through security screening a second time, because of what the airport called a low-level security threat.
Border Control and the police worked with the staff to respond to the threat, and to keep disruption to a minimum.
Mr Clay apologised for the inconvenience caused.
All disrupted flights had departed by 5.15pm last night.
