Anyone who enters the ACT from COVID-19 affected areas of NSW from 11.59pm on Friday will be required to enter strict home quarantine for 14 days.
But the territory's requirements for people to wear masks in public will end as planned, with ACT health authorities satisfied the risk of community transmission has fallen in Canberra.
Anyone who enters the ACT from Greater Sydney, Blue Mountains, Central Coast, Wollongong and Shellharbour after 11.59pm on Friday will need to complete an online exemption form prior to travel and quarantine immediately on arrival.
ACT residents will automatically receive an exemption and be supported to safely return to their homes, ACT Health said.
Exemptions for non-residents will only be approved in highly exceptional circumstances.
"Even if an exemption is approved, people receiving an exemption will be required to quarantine. If people do not have suitable premises to quarantine in, they will be required to quarantine in a hotel at their own expense," ACT Health said.
People under quarantine orders will not be allowed to leave their home for any other reason other than in an emergency or to seek essential medical care.
"If you cannot maintain appropriate separation from other members of your household, they will be required to quarantine in your home with you, or you will need to quarantine in a hotel or other approved premises at your own expense," ACT Health said.
The move to impose quarantine orders comes as the ACT looks to shore up its response to the fast-evolving coronavirus outbreak in Sydney, where the NSW state government has imposed tougher lockdown measures.
However, ACT Health Minister Rachel Stephen-Smith said the reduced number of people travelling from Greater Sydney to the ACT meant the risk of community transmission in the territory had dropped, giving the government confidence to wind back mask-wearing rules.
But concern has increased that people who do return from Sydney are more likely to be infectious.
The health minister said home quarantine requirements would allow for greater enforcement.
"Obviously, if someone is required to be at home all the time, the police can go and knock on their door and if they're not there, that's clearly a breach," Ms Stephen-Smith said.
Health officials would also begin stringently enforce criteria before issuing exemptions to non-residents seeking to come to the ACT from Greater Sydney.
"It is going to be harder to get that exemption than it has been, potentially, over the last couple of weeks. Those criteria are going to be applied really strictly considering the circumstances that are in place in Sydney," Ms Stephen-Smith said.
Non-ACT residents are currently banned from entering the territory from Greater Sydney.
ACT residents returning to the territory from Greater Sydney have been required to make a declaration to ACT Health and complete a 14-day period under stay-at-home orders.
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Ms Stephen-Smith said the ACT would still relax its mask-wearing rules, despite NSW recording 44 cases of COVID-19 with more than half infectious in the community to 8pm on Thursday.
"The thing that's driving the capacity to lift the mask mandate is that reduction in the number of people who are travelling, so that is actually seeing a reduction in the risk of the number of people who could potentially bring the virus into the ACT," she said.
ACT Health said mask wearing would still be encouraged and Canberrans should be prepared for the rules to change at short notice.
"While masks will no longer be mandatory, the government is still encouraging their use in spaces where physical distancing is not possible, such as public transport or crowded venues," ACT Health said.
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