There's a new ban on non-essential indoor gatherings of more than 100 people, and panic buying has reached such levels that supermarkets are asking for calm from customers and have announced new opening hours.

We look at what governments and experts are saying about some of the latest changes as the response to COVID-19 keeps unfolding.

First of all, we should look at what's meant by "indoor". The federal government's been pretty clear, saying it refers to a gathering within a single enclosed area.

So that's an area, room or premises "substantially enclosed by a roof and walls, regardless of whether the roof or walls or any part of them are permanent, temporary, open or closed".

Next, Prime Minister Scott Morrison has listed the indoor gatherings that are considered essential and therefore are allowed: airports, medical and health service facilities, pharmacies, correctional facilities, courts or tribunals, parliaments, food markets, supermarkets and grocery stores, shopping centres, office buildings, factories, construction sites, mining sites, emergency service facilities, disability facilities and public transportation facilities such as stations, platform, stops, trains, trams and buses.

Aged care facilities are also considered essential, but the government has announced restrictions on visits to them.

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Asked about churches, mosques, synagogues and other religious gathering places, Mr Morrison said they must comply with the rule of no more than 100 people at an indoor gathering.

States and territories will give more consideration to practical guidance and rules for non-essential indoor gatherings of fewer than 100 people (including staff) such as cinemas, theatres, restaurants and cafes, pubs, clubs, weddings and funerals.

Mr Morrison said this will be considered at the next national cabinet meeting on Friday. "In the meantime these venues should continue to apply social distancing and hygiene practices," he said.

The ACT government said indoor gatherings of more than 100 people no longer allowed may include:

Gyms, indoor fitness centres and swimming pools don't have to close at this time, providing they meet requirements for social distancing and hand hygiene.

"Such venues should take actions to ensure regular high standards of environmental cleaning take place," Mr Morrison said in a statement on Wednesday.

The ACT government has said yes, it is still safe to swim in pools. It advises people to practice good general hygiene and hand hygiene, and to stay home if they are sick.

University of New South Wales epidemiology professor Mary-Louise McLaws said that given how public pools are super-chlorinated, and automatically, continuously chlorinated, it was unlikely that the SARS-Cov-2 (that causes COVID-19) could survive in them.

No. The message from governments is do not bulk buy, panic buy or stockpile, whatever it's called. Governments and the experts are both clear on this. Mr Morrison gave Australians who have gone out panic buying a chiding today, saying it was not sensible, not necessary and not helpful.

"I've got to say it's been one of the most disappointing things I've seen in Australian behaviour in response to this crisis," he said.

In fact, it's actually distracted from efforts to deal with COVID-19.

ACT Chief Minister Andrew Barr said 98 per cent of the products on shelves are produced in Australia, and that supermarkets won't be shut down for weeks at a time, so there's no need to panic buy.

Monash University lecturer in international business and economics Dr Giovanni Di Lieto said there's no reason to panic buy and that the basic essentials of everyday life would remain available. Chickens would still lay eggs, cows would still produce milk, and someone would need to keep buying these.

In Italy, the European country worst-hit by COVID-19, there was no shortage of food or fresh produce and people were still able to go shopping, he said.

Have you watched people walk out the supermarket doors with lots of toilet paper and wondered why? It's something that psychologists and economists will no doubt study for years after the COVID-19 pandemic passes.

Monash University consumer psychology researcher Professor Hean Tat Keh said panic buying was a symptom of decision-making under uncertainty.

"In general, members of the public who are not well-informed about COVID-19 are getting bits and pieces of information about this new epidemic," he said.

"The lack of a full picture drives the fear of the unknown. That is, consumers are not sure what to expect, how the situation will further evolve and how their lives will be affected.

"So, when they go to the store and see other shoppers filling up their trolleys, these consumers will do the same, thus fuelling panic buying."

The "herd mentality" involved is a case of FOMO, or Fear of Missing Out.

Dr Di Lieto said panic buying was a self-fulfilling prophecy, when a person or a group believes something will happen, and then behaves in a way that causes it to happen.

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