Queensland authorities are on alert after a man with COVID-19 flew between Brisbane and Perth last week.
Chief Health Officer Jeannette Young says the man initially arrived in Brisbane on a flight from the Philippines via Papua New Guinea on July 3 and entered hotel quarantine.
After 14 days and three negative tests, he flew to Perth on July 17 or 18, where he was denied entry and put into hotel quarantine.
The man was then put on Qantas flight 932, which arrived in Brisbane at 12.55pm on July 20.
He became unwell while staying a backpackers hostel in Brisbane and tested positive for the Alpha variant of COVID-19 on Monday.
Dr Young says authorities are tracking down other passengers on the flight and hostel guests.
"I'm glad that this is Alpha," she told reporters on Thursday.
"It's still a significant risk and we still need to track through everyone who has been at that hotel, but I'm confident that hotel has very good records and will be able to find everyone."
Genomic sequencing matches the man's case with three people who were on the same flight from PNG to Brisbane on July 3.
"That is a longer incubation period than we would normally expect, but we know around one per cent of people can have an incubation period longer than 14 days, as has happened with this gentleman," Dr Young said.
WA Health also tested the man for COVID-19 and Queensland was seeking those results to confirm the man's infectious period.
"We don't believe at this stage it represents any risk to the WA public," WA Health Minister Roger Cook said.
"But it is obviously concerning that we have had another case now where someone has left hotel quarantine and then become positive for COVID-19."
Authorities have tested 62 guests at the Brisbane City Backpackers HQ and the neighbouring Joe's Place Backpackers.
Dr Young said 59 tests were negative for COVID-19 while results were pending on three others.
However, one man was taken away from one of the hostels in an ambulance on Thursday afternoon.
The others guests remain quarantined inside the hostels, which are being guarded by police.
Queensland Health Minister Yvette D'Ath said the face mask mandate would continue in the southeast for another seven days.
"We're up to 13 incursions of the virus through different outbreaks in Queensland over the last six weeks," she said.
"We have been able to contain all of these outbreaks to very small numbers, and that is in no small part due to the restrictions we've had in place."
Meanwhile, genomic testing has revealed a Gold Coast man recorded as a COVID-19 case on Monday picked up the Delta strain in hotel quarantine.
Dr Young said the only way to stop Delta breaches was with purpose-built quarantine facilities where rooms could be accessed from outdoors rather than enclosed corridors.
"That's really the next step, and as people are aware that's what the Queensland government has been asking for for many, many months now," she said.
Authorities have also transferred 10 COVID-19 patients from a ship docked at Weipa, in the state's far north, to Brisbane hospitals for treatment.
Eleven crew members remain on board MV Sanyu; nine are positive COVID-19 cases and two have tested negative.
Queensland recorded no new locally acquired cases of COVID-19 and one new case in hotel quarantine on Thursday.
Australian Associated Press