Qantas and Jetstar will scale back flights for Australia's most prolific domestic route due to the closure of the NSW-Victoria border.
The airline announced on Monday it would significantly reduce flights to and from Melbourne after NSW Premier Gladys Berejiklian and Victorian Premier Daniel Andrews agreed to indefinitely shut the border.
Qantas said the Sydney to Melbourne route, which was rated the world's second-busiest in 2018 with 54,102 departures annually, would be most impacted.
Its low-cost carrier, Jetstar, had recently ramped up flights on the route as COVID-19 restrictions eased, even removing social distancing between seats to increase capacity.
But the border closure from 11.59pm on Tuesday has forced the airline to slam on the brakes, with a return to limited flights for essential travel only.
Other routes will also be affected including flights from Melbourne to Byron Bay and vice versa.
The reduced schedule is set to operate for the rest of July.
Qantas will contact customers who have already booked airfares to and from the Victorian capital.
"We're going to reach out to them to offer them a range of options whether it's a change of date, or a voucher or a refund," a Jetstar spokesman told AAP.
Virgin Australia, still under the control of administrator Deloitte ahead of its proposed sale to US private equity giant Bain, is reviewing its Sydney to Melbourne flight schedule but is yet to make any amendments.
"We'll contact passengers directly if there's any change to their flight," a spokeswoman said on Monday.
Australian Associated Press