Millions of people in southeast Queensland, Townsville, Magnetic Island and Palm Island are in lockdown on Thursday amid five separate virus outbreaks, including three involving the more contagious Delta strain.

Premier Annastacia Palaszczuk says one of the new cases is linked to the Portuguese club cluster, while the other is a Qatar Airways check-in desk worker at Brisbane Airport.

The discovery of two new local cases, after more than 28,000 tests, is encouraging news for Queenslanders hoping the lockdown will end at 6pm on Friday, as originally scheduled.

"We've still got another 24 hours to go to see what happens over the next 24 hours, and we'll update you tomorrow in relation to whether or not we can leave that lockdown," the premier said.

"But like I said, it is very, very encouraging for us, at this stage."

Chief Health Officer Jeannette Young said the Qatar Airways worker had been symptomatic since Sunday, meaning she'd been infectious in the community since last Friday.

The woman in her 30s lives with another person, who is also being tested.

The worker visited an Officeworks in North Lakes, a Coles supermarket at Murrumba Downs and was a regular at Anytime Fitness in Griffin.

Dr Young said the woman likely contracted the virus at the airport, where she was checking in passengers while being exposed to flight crew members.

"We don't always know which of them are positive, which is why I really and truly insist people must wear masks at the international airport, and our domestic airports, that is really critical," she said.

While she is confident about each of the state's COVID incidents individually, Dr Young said managing all of them simultaneously "is a lot" and "we'll just have to see how we go".

As well as the Portuguese club cluster, the airport worker and a hospital receptionist, the state is managing the case of a worker who returned from an NT mine and potential contacts of a Virgin crew member onboard several flights while infectious.

Queensland also recorded two cases acquired overseas amid calls for a dramatic reduction in the number of overseas arrivals putting strain on it's hotel quarantine system.

It comes as Health Minister Yvette D'Ath appoints a private doctor to lead a probe into why a 19-year-old clerical worker, who caught the Delta strain while working outside a COVID-19 ward, wasn't vaccinated.

Mater Health Infectious Diseases Physician Paul Griffin will look into what happened at the Prince Charles Hospital, she says.

The government has also written to five major hospitals to ask why vaccinations shouldn't be expanded to all staff working at sites with COVID wards.

"Every time we have had transmission we have looked at how we can improve our processes," Ms D'Ath said.

"Every jurisdiction has done this, that has had an outbreak, whether in hotel quarantine or in our hospital system, to learn the lessons of what we can do better, but also to look at the changing nature of these variants and the risk profile."

Meanwhile, Dr Young defended her advice for under 40s not to get the AstraZeneca vaccine, but wait for Pfizer, due the extremely low risk of an extraordinarily rare blood clotting disorder.

"I have put my advice out there very, very clearly. Now, people need to work out where they want to get advice from," she said.

The premier also denied her tweet falsely claiming that the UK government "won't allow" under 40s to get the AstraZeneca vaccine had been misleading.

She later tweeted a link to a BBC article that says 18-39-year-olds in the UK will be "given an alternative" to AstraZeneca "if available, and if it does not cause delays in having the vaccine".

The article also states immunisation is estimated to have saved 10,000 lives in the UK.

Opposition Leader David Crisafulli said Dr Young was giving health advice in good faith, but he accused the premier of misleading people about vaccines to score political points.

"(She's) using information to try and weaponize the debate, making up stuff about whether or not the federal government is planning mass vaccination hubs, Googling, becoming Dr Google, on what's happening in the UK, and then providing that as factual advice," he said.

Australian Associated Press