The partner of the Brisbane cleaner who tested positive to the UK COVID-19 variant has also become infected, but the city's lockdown won't be extended.
Chief Health Officer Dr Jeannette Young says the man has been in quarantine since 7 January and additional contact tracing is underway.
"We know this particular variant of COVID-19 is more contagious, so this result is unsurprising," she said.
"However it highlights the importance of why the Greater Brisbane lockdown was so important to ensure any potential spread of the virus is contained."
Genome sequencing is being conducted but it is likely to be the UK variant. Additional testing of other close contacts of both the man and woman will continue this week.
There is no change to the restrictions which mark the conclusion of Greater Brisbane's lockdown.
Face masks were to remain mandatory but residents of Brisbane, Logan, Ipswich, Moreton Bay and Redlands allowed to leave home without reason from 6pm.
The three-day lockdown appears to have contained the highly contagious UK strain of COVID-19 with no new cases of community transmission reported since Friday.
"Can I thank people in the greater Brisbane region for responding in the way that they did? It has been absolutely, truly remarkable," Premier Annastacia Palaszczuk told reporters on Monday.
People must carry a face mask at all times for the net 10 days and wear them in indoor venues such as shops, hospitals, places of worship, libraries, cinemas, art galleries and gyms.
They are not required inside homes, restaurants or bars, or other places where people can socially-distance.
Dr Young says the lockdown allowed contact-tracers to find 370 close contacts of the cleaner.
She said 172 had already tested negative and the others were either getting tested or awaiting results.
Dr Young is still trying to find "less risky contacts" who visited three venues at the same time as the woman last week.
They include Woolworths at Calamvale North between 11am and 12pm on 3 January, Coles Sunnybank Hills Shoppingtown between 7.30am and 8am on 5 January and a Sunnybank Hills newsagent between 8am and 8.15am on 5 January.
"I'm not sure we've found everyone who attended those three venues yet," Dr Young said.
"So it's really important that anyone who has attended one of those three particular venues ... comes forward."
Chamber of Commerce and Industry Queensland's Amanda Rohan said the lockdown and the new rules were a setback for businesses during the crucial school holiday trading period.
She urged people to get out and support businesses while abiding by the new rules.
"What needs to happen now, is to know how we can prevent any future immediate shutdowns to avoid this uncertainty again," Ms Rohan said.
Opposition Leader David Crisafulli said the lockdown created uncertainty for business but it was a relief to see there were no new virus cases.
He said the police probe into the quarantine breach was crucial so that the overall system can be strengthened and future mistakes minimised.
Dr Young urged people to get tested, particularly in the Calamvale North and Algester areas, after 18,904 tests were conducted on Sunday.
Four new virus cases were reported in hotel quarantine on Monday - two Emirates crew members and two passengers who had arrived from the UAE.
Two of those people had travelled to the UK, but Dr Young said it was too early to know if they had the more contagious strain of the virus.
Relaxed border restrictions
People from Greater Brisbane will now be able to travel to the ACT, the Northern Territory and Tasmania without restrictions after the state and territories revoked their classification of the region as a COVID-19 hotspot on Monday.
Arrivals to the ACT from the Brisbane region had since Friday been ordered to self-isolate while ACT residents in Brisbane were told to stay put rather than travel home.
Today's decision to remove isolation requirements means around 4,800 people currently quarantining in Canberra have been let out early.
Anyone arriving to the NT from Brisbane from Friday had been required to enter mandatory supervised quarantine.
There are currently 400 people in supervised quarantine at the Howard Springs facility outside Darwin who will now be able to leave, NT Chief Minister Michael Gunner told the media on Monday afternoon.
"The key reason we can remove the hotspot is there has been no community transmission," Mr Gunner said. "The precautions Queenslanders will take for the next 10 days with masks gives us extra confidence."
The chief minister also said the NT had agreed to gradually increase its number of international arrivals from 500 to 850 per fortnight over the coming weeks, with costs to be covered by the federal government.
Tasmania also allowed several thousand people who had arrived from Greater Brisbane before 9am on 8 January out of quarantine on Monday.
Anyone who has arrived since then is still required to complete 14 days in self-isolation, with the Brisbane region remaining on the high-risk list.
Health Minister Sarah Courtney said their quarantine requirements will be reviewed in two days.
People in Australia must stay at least 1.5 metres away from others. Check your jurisdiction's restrictions on gathering limits.
If you are experiencing cold or flu symptoms, stay home and arrange a test by calling your doctor or contact the Coronavirus Health Information Hotline on 1800 020 080. News and information is available in 63 languages at .
Please check the relevant guidelines for your state or territory: , , , , , , , .
