Queensland's Chief Health Officer Jeannette Young has expressed concern after routine testing found COVID-19 fragments in wastewater at four locations.
The state recorded two new coronavirus cases on Tuesday, both of which were detected in hotel quarantine and acquired overseas.
Dr Young said the positive results collected on December 29 and 30 were particularly concerning because of outbreaks in NSW and Victoria.
She called on the Warwick, Stanthorpe, Loganholme and Cairns communities to get tested immediately if they have any COVID-19 symptom.
"A positive sewage result means that someone who has been infected was shedding the virus. Infected people can shed viral fragments and that shedding can happen for several weeks after the person is no longer infectious," Dr Young said.
"While this doesn't necessarily mean we have new cases of COVID-19 in these communities, I am treating this with absolute caution given the emerging situation across several other states."
There have been more than 20,000 tests in the past two days after a push for people who had been in Victoria since December 21 to get tested.
"Please remember, if your local testing clinic is crowded, consider attending another one," Dr Young said.
Public health directions have been issued banning people who have been in Victoria on or after December 21 from entering residential aged care facilities, disability accommodation and hospitals unless 14 days have passed.
Hospital visits are permitted if a negative COVID-19 test is obtained in Queensland.
