The passenger, who did not want to be named, said helicopters and other planes, including Virgin and Jetstar, have continued to leave since the note was found.
The planes that were taking off appeared to be empty.
"They are in fact planes that were ready to be boarded but weren't in the end," the passenger told the Herald.
James Grace, who works near the airport at Rent a Dent car rentals, said he had seen hundreds of people were crowded together on the carpark side of the building and around 100 more on the tarmac whom he thought had disembarked from two planes.
But it did not appear to him that the airport was closed, as he had seen two planes take off since the emergency began at around 3pm.
He had heard alarms and sirens but was unaware of the bomb message - until told by the Herald - and had thought the airport was going through some sort of fire drill.