But he added that he remained confident that security protocols at Australia's airports would have prevented the terror plot's success.
Mr Turnbull said the government had put in place additional security measures at Sydney airport on Thursday following advice and had extended those and "further measures" to all domestic and worldwide terminals at major airports. In Sydney, queues spilled out the door at the T2 domestic terminal and onto the footpath this morning.
While the lines are reportedly being dealt with efficiently, travellers nationwide have been asked to arrive at least two hours before their flight to allow for the delays.
Travellers flying on domestic flights were warned by carriers including Qantas to arrive at airports at least two hours before their scheduled domestic flight and three hours for global flights. "[Increased security measures] will be required for as long as the threat is assessed as requiring them".
But aviation and counter-terrorism experts warned "more needs to be done" to secure the nation's airports - including having passengers show photo ID before boarding domestic flights. It includes an increased police presence and additional screening of both carry-on and check-in luggage. Some measures will be obvious and others will be covert.
On the one hand, you might get lucky and breeze through security and customs with minimal fuss, but the odds of that happening are, well. let's just say you should probably play it safe and rock up earlier.
The chief executive officer of Homeland Security Asia/Pacific, which consults to governments and corporations around the world, said potentially risky passengers could board under someone else's name.
The foiled Australian terrorist plot targeting an airline, believed to be inspired by ISIS, has gotten the attention of the U.S. Department of Homeland Security.
The national terrorism threat level was raised to "probable" in 2014 and the AFP said the alleged plot represented the "thirteenth significant threat".