It is a testament to the speed with which the Australian Defence Force can deploy that by Wednesday evening, the 37-year-old pilot was taking off in a C-130 transport plane from Al Minhad Air Base carrying 10 tonnes of food, water and supplies.

After a four-hour flight over the Persian Gulf and across strife-torn Iraq, and now under cover of darkness, they fell into a holding pattern with an international team of aircraft that included other transport planes, intelligence planes and close air support for protection.

The sheer complexity of so many planes from different countries, all having taken off from different bases across the region, made it ''one of the most challenging missions I've ever been involved with'', Squadron Leader Clark of the RAAF said.

But from the point of view of satisfying missions, the humanitarian aid to people fleeing the utterly brutal Islamic State group was ''a no-brainer''.

''It's an amazing feeling, this one, to be able to do such a complex mission with such an unambiguously good outcome,'' Squadron Leader Clark said.

US President Barack Obama credited the humanitarian drops as playing a role in helping thousands of Yazidis off Mount Sinjar by giving them the strength to walk down the north side of the mountain and towards the relative safety of Kurdish-controlled territory.

Further immediate air drop missions now look unlikely. But US military spokespeople as well as Prime Minister Tony Abbott are warning that further crises could emerge.

''The situation in Mount Sinjar itself has somewhat eased, but the overall security situation in Iraq remains perilous,'' Mr Abbott said on Friday. ''While I certainly don't envisage Australian combat troops in Iraq, we are consulting with our allies and partners on what Australia can usefully contribute to try to ensure that the situation in the Middle East improves rather than deteriorates.''

Moreover, US claims that the siege has been broken are being disputed. Vian Dakhil, an Iraqi member of Parliament and a Yazidi leader who raised the alarm a week ago, said a major crisis remained with 70,000 to 80,000 still trapped on the mountain. She was backed by the United Nations, whose spokesman in northern Iraq, David Swanson, said the crisis on the mountain was ''by no means over''.

''Although many people managed to escape from the north side, there are still thousands of others up there, under conditions of extreme heat, dehydration and imminent threat of attack. The situation is far from solved.''

Asked whether Australia might consider a limited troop deployment for a humanitarian mission - say, if large numbers of refugees again came under threat - Mr Abbott refused to answer directly but said Australia would continue to uphold its humanitarian principles.