A pop-up clinic at Dickson College provided additional capacity on Saturday and Sunday but wait times at some sites stretched beyond two hours.

But more pop-up testing sites will be considered on a daily basis in the lead up to Christmas, health authorities have confirmed.

It comes as the new drive-through site in Mitchell struggled to keep up with demand and closed more than five hours early due to wet weather.

It had replaced the much larger EPIC drive-through clinic that had been operating for nearly two years and was closed down on Saturday.

Some reported being turned away on Sunday morning and told to head to other clinics. Updates throughout the day showed wait times exceeded two hours.

Canberra Health Services said the site was able process around 100 cars an hour and had undertaken 1255 tests on its first day, despite having to pause while Canberra was hit by a damaging storm.

The Kambah drive-through site, in the ACT's south-west, also has people queuing for more than an hour at certain times.

ACT Health recommended people attend the Dickson and Garran sites though wait times varied throughout the day.

Health authorities had earlier said they felt confident the downsized Mitchell site would still be able to keep up with demand.

The health services' chief operating officer Cathie O'Neill said she believed around 60 per cent of those coming through to get tested were doing so for domestic travel.

It was likely to drop again soon as the holiday period neared closer, she said.

"The issue for us is when Canberrans all decide to get there before we've even opened and that's when the queuing starts," Ms O'Neill said

"So we would really encourage people just to spread their visit out through the day, because if the flow's constant, then we get through everyone without anybody having to wait."

The nation's capital recorded 18 new cases of COVID-19 for a second day in a row on Sunday.

There are now 103 active cases in Canberra with three of those in hospital.

In NSW, the record for the highest number of daily infections within any Australian state or territory since the pandemic began was broken for a second day in a row as 2566 infections were reported.

The growing numbers have experts concerned with pressure on state and territory leaders to reintroduce face mask-wearing mandates.

The federal deputy chief medical officer Dr Sonya Bennett cautioned Australians to continue wearing masks inside even if it was no longer mandated.

"I'd probably encourage everyone to think about continuing to wear masks, particularly in settings that are indoor, public indoor spaces that may not be well-ventilated," she said on Sunday morning.

"Think about wearing a mask. It's a simple, easy thing to do.

"We know at Christmas time the shops do get very crowded. I was there myself yesterday. It was really pleasing to see, you know, a large proportion of people still wearing masks. But probably not large enough.

"I didn't have [my mask], but it reminded me that in the future I will certainly be taking a mask to anywhere that's crowded, particularly around Christmas time, because it's an effective, another effective layer of protection."

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