While the UK prepares to exit lockdown and the coronavirus vaccination continues apace, the Australian government remains cautious on the prospects of reopening international travel corridors.

And, with half of the 16 competing nations due to arrive from the southern hemisphere, that is presenting a major headache for organisers of the 16th World Cup in the UK in October and November.

Although Australia are on track to fully vaccinate their population by the end of the year, Tuesday's federal budget warned that the borders will remain largely closed and normal international flights will not resume until mid-2022.

"With respect to international borders, it's quite a conservative, cautious assumption that international borders will gradually reopen from the middle of next year," said treasurer Josh Frydenberg in his budget speech.

A prolonged ban on international flights will affect players coming from New Zealand, Fiji, Tonga, Samoa, the Cook Islands and Papua New Guinea as well as Lebanon and Australia who, even if they were permitted to travel, would have to enter quarantine on their return.

A World Cup spokesman said: "RLWC2021 recognise that there are still challenges ahead but we will continue to work relentlessly with an overwhelming desire to deliver the biggest and best ever Rugby League World Cup later this year.

"We remain extremely hopeful and optimistic that the tournament will go ahead as planned but we are realistic about the challenges, not least those which involve international travel and quarantine and are reviewing the various scenarios on a regular basis with all stakeholders.

"We will not be making any definite decisions before we have a clear and informed view of the landscape ahead - both domestically and internationally."

Australian Associated Press