Health authorities are also continuing to monitor the need to reintroduce mask-wearing requirements and limit visitors to high-risk settings, including aged care facilities, but the ACT's domestic health restrictions remained unchanged on Monday.

The three-day quarantine period for international arrivals will be dropped from 11.59pm on Monday, with people arriving in the ACT instead required to get a polymerase chain reaction COVID test and isolate until they return a negative result.

Health Minister Rachel Stephen-Smith said the changes would bring the ACT into line with new settings for international travel in NSW and Victoria.

"Travellers will still need to complete the online declaration form within 48 hours prior to travel to the ACT, get an additional test after day six after arrival, and must not enter a high-risk setting until 14 days have passed since their arrival in Australia," Ms Stephen-Smith said.

"And of course international arrivals who are not fully vaccinated still need to undertake the mandatory 14-day hotel quarantine at their port of arrival."

The 72-hour quarantine period for all international arrivals was introduced in late November at the same time as two-week quarantine for travellers from a series of African countries in a bid to prevent the Omicron variant from reaching the ACT.

The first Omicron case was reported in the ACT on December 3.

Health authorities have again warned the ACT could experience a spike in the number of COVID-19 cases, including Omicron variant cases, as a result of increases in travel and the number of gatherings held over the Christmas period.

Ms Stephen-Smith said not attending venues of the kind that had been identified as close contact exposure sites, such as gyms and nightclubs, would help keep people safe.

"If you want to be very safe and protect yourself in the lead up to Christmas and the new year, think about the places you're going as well as wearing a mask in an indoor setting where you're not able to physically distance from others," she said.

There have been 40 Omicron cases of COVID-19 identified in the ACT, with more than 200 people in isolation as a result of coming into close contact of a case. Further genomic sequencing is expected to identify more Omicron cases.

Government-run clinics have continued to be inundated with high demand for PCR COVID tests, as waiting times were consistently above two hours at most sites on Monday.

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Ms Stephen-Smith said about half of the people presenting for tests needed them to travel interstate, a requirement imposed by some jurisdictions which had driven up demand around the country in the lead-up to Christmas, but there was no need to run separate clinics.

"Throughout the life of the testing clinics we have looked at differentiating lines for various purposes. There is a fast-track line for healthcare staff who do need to get tested quickly so we can understand any potential exposures. But other than that, it doesn't necessarily make a lot of difference in the timeliness of people getting tested," Ms Stephen-Smith said.

The Health Minister defended the new Mitchell clinic, which on Saturday replaced a larger drive-through centre at Exhibition Park, saying it had processed a record number of tests. Garran also processed a record number of tests at the weekend, Ms Stephen-Smith said.

The Mitchell drive-through clinic reached capacity at 9.30am on Monday, ACT Health said in a social media post. "If you were planning to go to Mitchell, please consider visiting Holt or Nicholls or returning to Mitchell in the early afternoon. Thanks for your patience," the post said.

Health authorities received 4025 negative test results in the 24 hours to 9am on Monday.

There were 13 new cases of COVID-19 reported in the ACT in the 24 hours to 8pm on Sunday. This is a slight fall from the previous 24-hours when 18 cases were recorded.

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