The ACT Government has confirmed a third case of coronavirus, as panicked Canberrans drive up to an hour-and-a-half away to buy groceries.

Key points: The third confirmed case in Canberra is a woman in her 70s who tested positive last night

The third confirmed case in Canberra is a woman in her 70s who tested positive last night As of 8:00am today, 1,389 people in the ACT have returned negative tests for the disease

As of 8:00am today, 1,389 people in the ACT have returned negative tests for the disease The two earlier confirmed COVID-19 cases both involved men in their 30s

The woman who tested positive to COVID-19 is aged in her 70s, and was admitted to Canberra Hospital last night.

It is believed she was infectious while on a Garuda Indonesia flight GA712 from Jakarta to Sydney, which landed on Saturday morning, March 14.

The woman then boarded a Murrays bus from Sydney airport to Canberra at 12.25pm that day.

ACT Chief Health Officer Kerryn Coleman said she was working with the airline and coach service to find other people who might have been exposed.

The woman wore a mask while on the bus, and Dr Coleman said that action "greatly reduced the risk" of spreading the virus.

"We still believe there is a small increased risk of exposure to people travelling on that bus," she said.

"Anything over two hours in a closely confined room is what we consider an increased risk."

Dr Coleman said health officials would try to alert people who might have been in close contact with the woman.

She added Canberra remained in an "excellent position" generally to contain the disease, especially given the challenges facing other cities.

"We certainly don't have community transition in the ACT at the moment," she said.

"There's no area that should be avoided."

The ACT was the last state or territory to confirm a case of the disease. The two earlier cases both involved men in their 30s.

As of 8:00am today, 1,389 people in Canberra had returned negative tests for COVID-19.

Canberrans targeting regional grocers

Supermarkets in Crookwell have been cleaned out by locals and people travelling from Canberra. ( ABC News: Adam Kennedy )

The third confirmed case of COVID-19 coincides with continued panic buying in ACT supermarkets.

Empty shelves and out-of-stock items have reportedly led some Canberrans to drive up to an hour-and-a-half away to stockpile food and groceries.

Some stores in regional towns report they are now cracking down on the visitors by imposing limits on what they buy.

Floyd Davies, who co-owns a small supermarket in Crookwell, about 130 kilometres north of Canberra, said he was seriously concerned that he could not supply his community.

"There are people from Canberra coming over and a significant amount from Goulburn, which is 30 minutes away, to do their shopping," he said.

"We know lots of the other owners and everyone is in the same boat — I don't think there is a supermarket that we know of that hasn't been stretched to the limits in terms of staff, in terms of stock.

"We're just not quite sure how long supply will last."

Crookwell locals stopping by for supplies were disappointed to find bare shelves.

"It's ridiculous. It's really ridiculous. I'm sort of ashamed of my fellow Australians at the moment, it's not good," one local said.

Another said it was hard to know how to manage the situation.

"Being a local, we kind of know most of our local people, but when strangers come in you can't sort of say, 'oh, you're from out of town, you can't shop here.'"

Meat, pasta, rice and vegetables are out of stock in many supermarkets across Canberra. ( Supplied )

However, Woolworths chief executive Brad Banducci said Australia does not have a food shortage.

"We have enough product in Australia to feed all of our customers," he told ABC Radio Melbourne's Mornings host Virginia Trioli.

"What we're experiencing at the moment is [not] the equivalent of feeding 24 million Australians, but trying to feed 50 million Australians and that's where the issue lies."

Woolworths joined other major supermarket chains today in urging shoppers to treat their staff with respect, in light of the recent fights over products breaking out in stores.

Aldi, Coles, Woolworths and IGA paid for full-page advertisements in many newspapers to tell readers they were doing "everything possible" to maintain stock levels.

"So we ask you to please be considerate in the way you shop …" the advertisement read.

"No one working or shopping in any of our stores should experience abuse or aggressive behaviour."

Canberra shoppers have hoarded certain foods, such as mince and pasta, but left others. ( Supplied )

The supermarket giants also urged shoppers to buy only what they needed, saying "it helps everyone, especially the elderly and people with disability".

Prime Minister Scott Morrison also pleaded with Australians to stop buying more than they needed at supermarkets in a press conference this morning.

"Stop hoarding. I can't be more blunt about it," he said.

"It is not sensible, it is not helpful, and it has been one of the most disappointing things I have seen in Australian behaviour in response to this crisis."