Sydney Airport's Qantas terminal was evacuated on Wednesday due to a security breach which saw 44 passengers of a QantasLink flight from Wagga Wagga allowed into the terminal despite not having passed through security.

As security screening is not carried out in Wagga Wagga, passengers normally are bussed to Terminal 2 for screening, but, according to a Qantas spokesperson, on Wednesday the bus didn't turn up and some passengers were allowed straight into Terminal 3.

"This was a process error on Qantas' part," the Qantas spokesperson said.

Terminal procedure requires an automatic evacuation if any unscreened passengers enter the "sterile area of the terminal" so that all passengers can be re-screened. 

Wednesday's evacuation took place at 2.25pm, re-screening commencing at 3.15pm and the terminal was back to normal operations by 4.00pm.

"We apologise for the inconvenience caused," the Qantas spokesperson said, as seven flights were delayed by up to one hour, adding the evacuation was a "necessary procedure".

"We take such incidents very seriously and are investigating how the breach was allowed to occur."

The breach reveals the poor quality of Australia's aviation security procedures as there is scant pre-flight screening in a number of the country's regional airports meaning security screening is done upon arrival into major airports, reported the Sydney Morning Herald.