The ACT has reported one new case of coronavirus, as plans to relax restrictions are put on hold.
ACT chief health officer Kerryn Coleman said it was likely more cases would be identified as hundreds of Canberrans return from Victoria to mandatory self-isolation.
The new case, a man in his 20s, is a close contact of one of three cases confirmed on Wednesday.
The government has advised anyone who has returned to the ACT from Melbourne before mandatory quarantine was introduced to self isolate for 14 days from the date they returned home.
"It's the one thing that people who have been in Melbourne ... can do to support this community," Chief Minister Andrew Barr said.
"If you have any symptoms get tested."
While infectious, the new case visited the Gungahlin Vodafone store on Monday July 6 between 3pm and 3.30pm.
Dr Coleman said the risk to the broader community was low, including to staff and the public who were in the Vodafone store at the same time.
However, anyone who attended this location during these times should monitor themselves for symptoms.
ACT Health is following up with management of the store.
It is the 112th case of coronavirus in the ACT, which had previously not recorded a new infection in more than one month.
On Wednesday, two men and a woman in their 20s tested positive for the virus, after two returned from a Melbourne hotspot last Thursday. The third person was a household contact.
Prior to being tested, the trio had visited the Fyshwick Markets on Saturday, July 4, between 3pm and 4pm, and Westfield Belconnen on Monday, July 6, between 12pm and 12.30pm.
One of them was a staff member at the yet-to-open burger venue Betty's Burgers, in the Canberra Centre, which will undergo deep cleaning.
Dr Coleman urged anyone who had been to those locations to be vigilant and get tested if they show any mild symptoms.
The four new cases are Gungahlin residents.
Anyone returning to the ACT from Victoria must now apply for an exemption and will be required to self-isolate for 14 days upon return, after the NSW-Victoria border closed at 12.01am on Wednesday.
The two people returned from a Melbourne hotspot before mandatory quarantine rules were put in place on Friday July 3.
Dr Coleman said more than 160 who had returned to the ACT were in self-isolation, with hundreds more applications lodged.
"It is possible there will be new cases emerging from these returning travellers in the coming weeks and we need to be in a position to respond quickly," she said.
Canberrans had been preparing to welcome the next stage of eased restrictions on Friday, however the increase in cases has forced the ACT government to rethink the move.
Restrictions will remain the same for at least two weeks, when they will be reviewed.
The next step would have allowed small hospitality venues to welcome up to 25 people, contact sports to resume play, gambling venues, strip clubs and brothels to reopen and outdoor gatherings of up to 250.
Dr Coleman said the full impact of the Victorian outbreak on the ACT was still unknown.
"The situation that is unfolding in Victoria is concerning and has resulted in four new confirmed cases in the last two days here in the ACT," Dr Coleman said.
"With the border restrictions here in the ACT and in NSW only coming into effect earlier this week, we need time to assess how effective they will be in slowing the spread of the virus.
"We currently have 168 people who have returned to the ACT and are now in quarantine either at home or in hotels and we are also working through approximately 400 requests to enter the ACT, from both residents and non-residents."
Dr Coleman said there had been negative commentary around the new cases and said no one was to blame for the increased numbers.
"The situation in Victoria is evolving very quickly, and people coming to the ACT who may have COVID-19 need our support," she said.
"We want to encourage anyone who has symptoms of COVID-19 to get tested and to know that if you do test positive for COVID-19 we will support you and do everything we can to ensure you get better."
Australian Medical Association ACT president Antonio Di Dio said people should now be reconsidering any travel they planned on taking.
"Last week and the week before we were talking about 'do we need to go to Melbourne'," he said.
"This week we should be talking about - do we need to go anywhere?
"Can it be put off, can we do it online instead?"
Dr Di Dio said he wanted clarity from the government about what constituted an essential worker, who are able to get exemptions to travel into the ACT from Melbourne.
He said arrangements for when school is due to return for third term also needed to be discussed.
"We need to be very vigorous on the social distancing, it's our only weapon," Dr Di Dio said.
"We should be very, very prepared for the advice [on restrictions and travel] to change twice a week for the next month or so."