The ACT government said on Friday that the test result had been recorded during the previous 24 hours.

The new case is not linked to the repatriation flight that brought about 120 Australians back to the ACT on Thursday.

According to authorities, the woman in question returned to Australia on Monday.

The diplomat flew into Sydney International Airport before travelling to the ACT in a private vehicle.

"She has followed all the correct processes and has been quarantining since her return to the ACT and is being supported by ACT Health," the government said in a statement.

"ACT Health has followed up with two close contacts of this individual and is managing them in accordance with national guidelines.

"While we believe the risk to these contacts is low, ACT Health continues to take a cautious approach.

"The circumstances of this new case demonstrates that our quarantine system here in the ACT is working well to protect the Canberra community from COVID-19."

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The diplomat is currently the only known active case in the ACT, which has now recorded 116 total coronavirus cases since the beginning of the pandemic.

The government said in its statement that three passengers on Thursday's repatriation flight had been tested at Canberra Airport, and each returned a negative result for COVID-19.

All of the people who were on the plane are now completing a 14-day hotel quarantine period.

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