An "onboard incident" on a Tigerair flight from Sydney to Melbourne led to the captain turning the flight around mid-flight and a referral to police.
Flight number TT271 was near the Victorian border at about 8pm on Monday evening when the flight turned back to Sydney.
Tigerair said the captain decided to turn the flight around "following an incident onboard".
Seven News reported that a threatening note was found.
"In line with standard procedures, the Australian Federal Police met the aircraft on arrival," Tigerair said in a statement to AAP.
"All guests and crew safely disembarked the aircraft and have been re-accommodated on the next available flight.
"We sincerely apologise for any inconvenience caused, however the safety of our crew and guests is always our highest priority."
One passenger, Lizzie, posted to Instagram that passengers were stuck on the plane for four to five hours with no food, water or access to a bathroom.
"We were not looked after at all," she said.
Another man praised Tigerair, Sydney Airport and federal police for handling "a really challenging situation well".
