Scott Morrison has defended using public money to fly former finance minister Mathias Cormann around Europe.
Mr Cormann has traversed the continent on a Royal Australian Air Force plane as he campaigns for a job with a global economic think tank.
The RAAF plane costs taxpayers more than $4000 per hour of flying.
The prime minister said the jet was being used because coronavirus was "running rampant" across Europe.
"There really wasn't the practical option to use commercial flights in the time we had available because of COVID," he told 2GB radio on Wednesday.
"If Mathias was flying around on commercial planes, he would have got COVID. The risk of that was extremely high."
Mr Morrison also justified the costly flights by arguing an Australian had never held a leadership role at the Organisation for Economic Co-operation and Development, more commonly known as the OECD.
"Now we're in the race for it and it will be very important," he said.
"Mathias would be an outstanding secretary-general of the OECD, standing up for those liberal, democratic, market-based values which the OECD represents."
Taxpayers are also funding a team of staff working 24/7 from the Department of Foreign Affairs and Trade to manage Mr Cormann's globetrotting campaign.
"A small temporary campaign task force has been set up to support Mathias Cormann as Australia's candidate for the secretary-general of the OECD," a DFAT spokesman told AAP.
"This team will return to other duties at the conclusion of the campaign in around March 2021.
"The task force consists of 8.5 dedicated staff, made up of a task force manager and campaign strategist, strategy and policy advisers, a visits manager, two graduates and a communications specialist."
The public servants are coordinating advocacy by senior government ministers, organising travel arrangements, and preparing campaign briefs and communications material.
Mr Cormann is being accompanied by one DFAT officer while overseas.
He is not being paid a salary by the Australian government.
The government is refusing to disclose the exact costs of his campaign until a successful candidate is chosen, claiming it could erode Australia's competitive edge.
There are 10 other candidates vying for the OECD position.
Since leaving Australia on November 8, Mr Cormann has met with key players in Turkey, Denmark, Germany, Switzerland, Slovenia, Luxembourg, Belgium, Spain and Portugal.
He is planning to meet decision-makers across other OECD countries over coming weeks, including in Austria, the Slovak Republic, Hungary, France, Chile, and Colombia.
In France, Mr Cormann will be interviewed for the position of secretary-general by OECD member state ambassadors.
Labor finance spokeswoman Katy Gallagher said the prime minister needed to be up front about what the campaign was costing taxpayers.
"And whether other options, such as a virtual campaign, were considered before agreeing to the exclusive use of one of Australia's RAAF aircraft and any other related costs," she told AAP.
Meanwhile, the Australian Greens have written to the ambassadors of OECD member nations warning them appointing Mr Cormann would be a blow to tackling climate change.
Australian Associated Press
Sign up for our newsletter to stay up to date.