A Vietnam Airlines pilot Monday refused to carry a Swede who had apparently joked about a bomb in his luggage.
The Australians, Prowse William James and Hansen Genevieve Mae, said they had overheard Lexander John Lennart saying something about having a bomb in his luggage while sitting near them at a café in Noi Bai International Airport.
They reported this an hour before they were scheduled to fly to Luang Prabang in Laos at noon.
Security officials then summoned all three of them for questioning and checked their luggage.
They were allowed to go after the checks turned up nothing.
But the pilot of their flight refused to carry them and the airline had to put the Australians on another flight six hours later and the Swede on one the next morning.
Vietnamese carriers have slapped fines and bans on local and foreign passengers earlier for making hoax bomb threats.