The Victorian government is refusing to apologise to Brisbane flight arrivals who claim health officials told them they would not be forced into hotel quarantine.
Greater Brisbane was declared a "red zone" under Victoria's traffic light permit system at 6pm on Monday.
About 30 interstate air passengers from Brisbane landed in Melbourne on Monday night after the border closed, but left on return flights on Tuesday.
AAP understands a further 15 remained behind, staying at Melbourne Airport's Park Royal hotel before being moved to the nearby Holiday Inn hotel on Wednesday afternoon.
Of that group, nine are expected to be released later on Wednesday evening pending a negative COVID-19 test result.
Sam was among those who spent two nights at the Park Royal after departing from Brisbane airport aboard a Qantas flight minutes before the city became a red zone.
He says he spoke to Victoria's Department of Health twice and was repeatedly assured his "orange zone" permit - allowing him to self-isolate and get tested within 72 hours of arrival - would stand as the flight was taking off before the 6pm cut-off.
"I boarded my flight at 5.35pm and I spoke to the DHHS at 5.15pm, who confirmed that I would not be going into hotel quarantine," he told Melbourne radio 3AW on Wednesday.
But when the plane landed, passengers were left waiting on the tarmac for two hours before each was interviewed.
It was then that Sam and an estimated 30 to 40 others were notified they would have to enter hotel quarantine because the plane landed after 6pm.
Sam says he would never have boarded the flight if not for the conflicting advice.
"Incredibly frustrated is a polite way of saying it," he said of the affair.
"I've done the quarantine before so I knew what I was in for, and I was incredibly angry."
Acting Police Minister Danny Pearson said a small number of interstate arrivals had been impacted by health directions changing while they were in the air.
"The government has got a clear responsibility to keep Victorians safe and we make no apology for that," he told reporters on Wednesday.
"We will protect our borders and we will protect our community."
Opposition Leader Michael O'Brien described the situation as an "absolute debacle" and said the government had not learned from the mistakes of previous snap border closures.
"When people contact the Victorian health department, they're entitled to get the right information. They're entitled to be told the truth," he said.
"These people were held at the airport for hours; no food, no water, couldn't even get a jumper out of their cases.
"These people have been put through absolute hell ... and it shouldn't be happening."
Earlier, Victoria's dedicated hotel quarantine agency confirmed the Holiday Inn at Melbourne Airport - the site of the state's most recent COVID-19 outbreak - had resumed operations on Wednesday.
International flights have been suspended in Victoria since February 13, when a hotel quarantine worker contracted the highly infectious UK virus strain from returned travellers at the Holiday Inn at Melbourne Airport.
The outbreak triggered the state's five-day, circuit-breaker lockdown, while the hotel was shut down for ventilation works.
International flights will resume on April 8, with arrivals capped at 800 a week, scaling up to 1120 by April 15.
Meanwhile, Victoria chalked up 33 days without a locally acquired case on Wednesday, from just over 22,000 tests.