Traces of coronavirus have been found during sewage testing at a treatment plant in Ipswich, raising the possibility of undetected COVID-19 cases.
Wastewater from the plant, west of Brisbane, returned a positive result for viral fragments during routine testing on Thursday, Queensland Health says.
Chief Health Officer Jeannette Young said the Ipswich result was concerning.
"Positive results from a month ago were most likely caused by virus shedding from a case that was no longer infectious," she said.
"(But) we are uncertain about the cause of the positive result."
Dr Young said the Ipswich wastewater facility had recorded several weeks of negative results after a series of locally acquired cases known as the Brisbane Youth Detention Centre cluster was brought under control.
"There is a very real possibility this wastewater result is a sign of one or more undetected positive COVID-19 cases in the Ipswich community, and we are treating this seriously," she said.
It comes as Premier Annastacia Palaszczuk accuses NSW counterpart Gladys Berejiklian of political meddling over comments about the border closure.
Earlier, Ms Berejiklian blasted Queensland for not taking enough returned overseas travellers while continuing to lock out most people from her state.
"Enough is enough. People are not able to get hospital treatment or access services on the other side of the border," she told reporters on Wednesday.
"Queensland expects us to process all their citizens ... but then just think of all these excuses as to why NSW residents can't move freely to their state.
"You can't have it both ways."
Ms Palaszczuk hit back later in the day, saying Queensland would not be lectured by NSW.
"We listen to the chief health officer," she said.
"It's disappointing to see the NSW premier try to be political at this time when she has enough of her own issues to deal with.
"People can try and play politics ... but it's no laughing matter. This is about people's lives, and about people's livelihoods."
Queensland recorded two new COVID-19 cases after a man, 45, and woman, 49, were diagnosed while in hotel quarantine in Cairns.
The man who recently returned from The Philippines, and the woman had been in Papua New Guinea.
Queensland last recorded a coronavirus case on Friday, when two infected crew members from a cargo ship anchored off the Sunshine Coast were transferred to hospital.
The state has five active cases, while health workers completed 4529 tests in the 24 hours to Wednesday morning.
It has been 48 days since the last COVID-19 case was diagnosed in the community.
Australian Associated Press