Although there are no COVID-19 cases in the ACT, health authorities are calling on the community to "be alert and be prepared for the situation to change".

ACT Health has reiterated that Canberrans should not travel to Greater Sydney while NSW faces a growing cluster with 18 news cases announced on Monday.

Several other jurisdictions are also tackling new cases in recent days.

"As there are more exposure locations being added every day, we strongly encourage people to reconsider their travel to other parts of Australia," ACT Health said in a statement.

"If you do choose to travel, you must abide by all public health directions in place in the state or territory you are travelling to, as well as the ACT.

"This may include changing your travel plans and adhering to public health instructions upon your return."

Queensland recorded two locally acquired cases which were out in the community and are under investigation.

Parts of the Northern Territory including Darwin started a 48-hour lockdown on Sunday after its first major community outbreak.

The Perth and Peel regions of Western Australia are under new restrictions after a woman returned home from NSW. One new case was recorded in WA on Monday.

South Australia has banned travellers from the ACT, WA, NT and NSW amid the recent increase of cases across the jurisdictions.

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Victoria has classified the ACT as an "orange zone" and now requires travellers from the ACT to apply for a permit, and agree to self-isolate, get a COVID-19 test and isolate until you get a negative result.

ACT Health urged anyone who has recently travelled to regularly check exposure sites on the ACT COVID-19 website, which is updated twice a day at 10am and 6pm.

"If you have recently travelled outside of the ACT you must check the ACT COVID-19 website twice a day and follow the health advice if you have been in any of the exposure locations," the statement read.

"If you are returning to the ACT please be extra vigilant when monitoring for symptoms of COVID-19 and get tested immediately if you experience even the mildest of symptoms."

The ACT government has responded to the growing COVID-19 threat interstate by mandating masks for many indoor settings.

Chief Minister Andrew Barr said the measure was "not a risk eliminator, but it's a risk reducer".

"Mask wearing applies across the border in Queanbeyan so there's not something magic in the air between the ACT and NSW," he said.

"I'd much rather be doing this ahead of the virus finding its way into the ACT then having to do it in a rushed way."

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