Thousands of prisoners across Queensland have been locked in their cells after a corrective services staff trainer tested positive to coronavirus.
The man, 60, didn't work in a prison but trained 14 prison officer recruits and came into contact with 11 other staff in the days before he was diagnosed.
Corrective Services Commissioner Peter Martin says about 7000 inmates from the central coast to southeast Queensland have been locked down.
"We've taken the very cautious step in concert with advice from Queensland Health to move to stage four, which is extreme isolation," he told reporters on Thursday.
The lockdown limits movement in and out of correctional facilities.
Prisoners will be confined to cells and receive no personal or professional visits. Staff who interact with them will wear protective clothing.
"These are very difficult times and our first priority is for the safety and security of those people in our custody and our care," Mr Martin said.
Corrections workers union secretary Alex Scott is concerned the lockdown will lead to more violence against workers but concedes it's the right decision.
"The alternative in relation to an outbreak of COVID within our centres would have been a tragedy for the staff and the inmates," he said.
The 25 staff the infected trainer interacted with have been tested and are now in quarantine.
The restrictions will remain until revoked by Chief Health Officer Jeannette Young.
Health Minister Steven Miles said there was no clear link between the infected trainer and the Brisbane youth detention centre coronavirus cluster.
However, the man lives in Forest Lake and works in Wacol.
"Both locations are where other cases from the Brisbane youth detention centre cluster are known to live or work," he said.
Eleven cases have been linked to the detention centre cluster.
Queensland's only other new virus case overnight was that of a man who had returned from Papua New Guinea.
He was diagnosed while in quarantine in Cairns and poses no risk to the community.
More than 40,000 people were tested for the virus in Queensland over the 48 hours to Thursday morning.
Mr Miles said genomic testing had not proved a solid link between the Brisbane youth detention centre cluster and one in Logan, south of Brisbane.
The Logan cluster started when two women went to Melbourne and returned to Queensland without quarantining.
Meanwhile, the skipper of a luxury yacht that sailed into the Gold Coast on Monday has been fined $4003 for breaching Queensland's border restrictions.
A criminal investigation was launched after seven people arrived from Victoria on the Lady Pamela superyacht.
Dr Young earlier granted the vessel and its crew an exemption to come to Queensland for routine maintenance and repairs.
A police investigation continues into allegations not all those on board were crew and the vessel stopped at NSW hotspots during its journey instead of quarantining.