Indoor gatherings of 100 or more banned

The ban applies to non-essential gatherings, so transport is not impacted and nor are health facilities. Prisons are not impacted by the ban, nor are workplaces including mining sites and supermarkets. Mr Morrison said they come under the definition of essential. Schools, childcare, universities and hotels are also not impacted by the ban.

But churches, mosques and other places of worship must comply, including with the 1.5 metre social distancing guideline, except among family groups, he said. Moving to online church services would be sensible, he said.

Outside, gatherings are allowed up to 500 people.

Chief Medical Officer Brendan Murphy said hand-shaking must now stop.

"No more hand-shaking, no more hugging, except in your family. No more scant attention to hand hygiene. Use hand sanitiser," he said.

More than two weeks ago, NSW Health Minister Brad Hazzard urged people to shop shaking hands, saying it was time for Australians to "give each other a pat on the back".

At the time Professor Murphy said hand-shaking was fine to continue except with people who had travelled overseas, but things have changed dramatically.

Australia now has 454 cases. On March 2, when Mr Hazzard urged an end to hand-shaking, it had 30 cases.

With three federal parliamentarians now diagnosed, Mr Morrison said he had been checked by his doctor last night but he would not be tested.

"I got a good tick last night from the doc. I appreciate that. But I intend to see him regularly in the weeks ahead," Mr Morrison said.

Home Affairs Minister Peter Dutton has the virus, and now a contact whom he saw on March 10 is also reportedly positive, exacerbating concerns about a Cabinet meeting Mr Dutton attended on March 10. But authorities insist that Mr Dutton was not infectious until March 11.

The government has upgraded its travel advice to the highest level for the first time.

"Do not travel abroad, do not go overseas," Mr Morrison said. "That is a very clear instruction. For those of you who were thinking of going overseas in the school holidays, don't."

Mr Morrison said domestic air travel was low risk. But he said people should not visit remote parts of the country, and the states and territories are set to impose travel bans.

New limits have been imposed on aged care.

Visitors to aged care homes have been limited to two people at a time, including professional visits.

Visits are only allowed in a resident's room or outside. Social activities and entertainment are banned in aged care homes and school groups are banned. No one aged 16 or younger is allowed in an aged care home without a special exemption. Mr Morrison said aged care homes can put in "very strict arrangements" on a case-by-case basis for visits when someone is dying.

Schools remain open.

"Whatever we do we have got to do for six months," Mr Morrison said.

If schools closed, tens of thousands of jobs would be lost, and the availability of health workers would be hit by 30 per cent, he said. "That will put peoples lives at risk. Let's keep our heads when it comes to this. "There is a national public interest here in keeping schools open. And our advice is it's not being done at the detriment of the health of any children."

Professor Murphy said in Hubei, only 2.4 per cent of the cases were in people under 19.

"We need to make sure that no sick child goes to school. We need to make sure that no sick teacher goes to school. We need to try and avoid large assemblies and other gatherings at schools,: he said, while acknowledging "it's not really possible for children in a classroom to keep 1.5m apart from each other".

"We've got to be practical about that," he said. "But schools should practice very good hand hygiene, too. Very hard to do in a school, but we can trust our teachers to do it. Children should be washing their hands regularly, particularly when they're eating and particularly when they're touching common areas. So it will be hard for schools, but it would be much, much, much harder for society if the schools were closed."

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Twenty thousand student nurses in Australia will be mobilised into the workforce, Mr Morrison said.

He warned that disruption would last at least six months.

"Life is changing in Australia as it is changing all around the world," he said.

"This is a once in 100-year type of event. We haven't seen this sort of thing in Australia since the end of the first world war."

With shortages of staples and supermarket shelves being stripped as they are stocked, Mr Morrison urged people to stop bulk-buying.

"Stop hoarding. I can't be more blunt about it. Stop it. It is not sensible, it is not helpful and it has been one of the most disappointing things I have seen

Stop doing it. It's ridiculous. It's unAustralian, and it must stop," he said.

The government is set to announce significant support for hospitality, tourism and air travel, with deputy Prime Minister Michael McCormack announcing that fees will be waived for the airline industry. The government has waived aviation fuel excise, Airservices charges for domestic travel and regional aviation security charges.

The total cost of the measures are estimated to be $715 million, with an upfront estimated benefit of $159 million to our airlines for reimbursement of applicable charges paid by domestic airlines since 1 February 2020.

Mr Morrison said the government 's measures were aimed to "keep Australia running, we are going to keep Australia functioning".

But he said there was "no too-weak answer to what we are confronting".

"Wherever possible we need to keep Australians working - working on the essential services and the economy that Australians need to get through this and this is a critical - a critical issue in ensuring Australia can keep functioning and, importantly, keep delivering the important services that are necessary which, at the end of the day, mean that we can support the most vulnerable in our community," Mr Morrison said.

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