The Morrison government in March announced 800,000 half-price flights to boost tourism in regions struggling because of the coronavirus pandemic.

With 663,000 airfares bought in two months, Deputy Prime Minister Michael McCormack remains open to extending the scheme.

"When those 800,000 tickets are gone, I'm very happy to look at what we can do in the future," he told Sky News on Thursday.

The federal transport minister said he would "quite potentially" release more cheap tickets when the allocation runs out.

"We'll look at Cairns, we'll look at places like Darwin, Kangaroo Island," Mr McCormack said.

"We'll see if the program has worked successfully as we wanted it to, and we'll also see the economics of those regions."

Consideration will be given to the flow-on effects for businesses in hospitality and other sectors, as well as the tourism industry.

All stakeholders initially panned the $1.2 billion cheap flight program with the exception of airlines, which welcomed the plan.

The government rejected claims the 15 select routes were mainly in marginal seats, instead pointing to a lack of international business numbers in those areas.

Darwin and Adelaide were added after the initial list was released.

In Queensland, the Gold Coast, the Sunshine Coast, Cairns, and the Whitsundays and Mackay region including Proserpine and Hamilton Island were included.

Uluru and Alice Springs in the NT, the Tasmanian towns of Launceston, Devonport and Burnie, Broome in WA, Avalon near Melbourne, Merimbula in NSW and SA's Kangaroo Island were also listed.

Meanwhile, Virgin has joined Qantas in pushing back its planned resumption of international flights from October to December.

The airlines made the decision after the federal budget assumed international travel would not resume until at least mid-2022.

Australian Associated Press