Queensland Premier Annastacia Palaszczuk said she was “very worried” and had not slept as she confirmed the cases were the highly-infectious UK strain.
The lockdown of greater Brisbane, starting from 5pm on Monday, includes the areas of Brisbane, Logan, Moreton Bay, Ipswich and Redlands.
Chief Health Officer Dr Jeannette Young described the spread as “significant”.
Seven cases have now been identified in the outbreak, which started three weeks ago when a doctor treating a COVID-19 patient was infected.
One of the cases is a brother of another person with the virus.
Two colleagues of the second new case have been infected. They were in Gladstone while infectious but are now in self-quarantine.
Late last night another case was diagnosed in a nurse working in a coronavirus ward.
Her sister also has the virus.
Dr Young said she did not know how the other two new cases were linked. She suggested one could be a housemate of another patient.
Ms Palaszczuk said the lockdown was a “protective measure”.
“I know this is a really big call. I know it is very tough but let’s do it now and let’s do it right,” the premier said.
“This is the UK strain. It is highly infectious. We need to do this now to avoid a longer lockdown and that lockdown will commence at 5pm this afternoon.
“This is a huge job now that we have to do because we have got more of this community transmission.”
Vaccinations must continue, government urges
The Federal government clarified that the lockdown does not prevent greater Brisbane residents leaving home to be vaccinated.
Health Minister Greg Hunt said the federal government had authorised asymptomatic testing across the Brisbane region, meaning people could be tested without symptoms.
The same asymptomatic testing has been approved in aged care facilities in the affected areas of Brisbane.
“At this stage there are no signs of any infections that have been transmitted to aged care but we are taking early, pre-emptive action,” Mr Hunt said.
“We know how to do this,” he said, talking about the lockdown.
Australia’s vaccination program was critical to stop further breakouts, he said.
More than 540,000 Australians have now been vaccinated, with more than 259,000 vaccinations in the past week.
‘This is the right thing’
Ms Palaszczuk earlier told Today the city would not enter a lockdown unless there were new untraced cases.
She has now told residents a lockdown is the best move to keep Queenslanders safe.
“I know this will mean some disruption to people’s lives but we’ve done this before, and we’ve got through it over those three days in the past, and if everyone does the right thing, I’m sure that we will be able to get through it again,” she said.
The Premier urged people not to panic-buy but that didn’t stop shoppers rushing supermarkets across the region and photos of shelves emptied of toilet paper filling social media.
Residents can stil leave home to shop under the lockdown rules.
The only other reasons to leave the house are for essential work, caring for a vulnerable person or exercise.
“They can go out and exercise in a family group or if they’re by themselves with one other person from a different family group,” Dr Young said.
People can have two visitors to their home.
Ms Palaszczuk said Scott Morrison had accepted her proposal to halve the rate of international arrivals to 1300 people a week.
“The halving of our international arrivals will also contribute to us being able to focus on the task at hand and hopefully after the three days we will be able to update Queenslanders,” she said.
She has urged all other state and territory leaders to declare greater Brisbane a hotspot.
Restrictions for all Queenslanders
Restrictions will not be limited to greater Brisbane. All Queenslanders are being asked to wear face masks and indoor gatherings have been capped.
“We will be putting in that compulsory mask wearing for the rest of Queensland and limiting gatherings to your own home to 30 people,” Ms Palaszczuk said.
“This is essential everyone that we do this to stop further transmission.
“We’ve seen what’s happened in other countries. I don’t want to see that happen to Queensland. I don’t want to see that happen to Australia. I know this is a really big call.
“I know it is really tough. We have Easter coming up, we have school holidays coming up but let’s do it now and let’s do it right and let’s see if we can.”