Health officials are encouraged Australia's coronavirus curve is flattening but insist the strict restrictions that have helped slow the infection rate must stay in place.

Deputy Chief Medical Officer Paul Kelly is also confident the nation's intensive care units won't be overwhelmed in the foreseeable future but warns that the virus won't be beaten without a vaccine which is possibly still 18 months away.

"I don't think we can eliminate this virus without a vaccine," he said.

AAP

So far, 4,860 people in Australia have caught the virus and the death toll has risen to 21.

But the average daily increase in cases has been at nine per cent for the past three days, down from 25-30 per cent a week ago, and the number of people needing intensive care remains well below 100.

Prof Kelly says while these are promising signs, the strict social distancing and business shutdown measures will need to remain in place, possibly for some months.

READ MORE Government relaxes JobKeeper criteria to allow startups to access wage subsidy

"In terms of the measures that have been introduced, I think there (are) good signs now that that is actually working as we had expected," he said on Wednesday.

"This is full credit to the Australian public who have really taken on enormous changes in their lives over the last few weeks."

Nevertheless, Prof Kelly warned winter was coming and with it the flu season, and it remained to be seen how that would affect the coronavirus epidemic.

All Australians are being urged to get a flu vaccination this year.

Earlier, his fellow Deputy Chief Medical Officer Nick Coatsworth said officials were treating the figures with caution.

"It's clear that we've landed a punch on COVID-19, but it's by no means on the canvas," he told Sky News.

Prof Kelly dismissed modelling published in the Medical Journal of Australia suggesting the country could run out of intensive care beds as soon as next week, saying it did not seem to be based on the Australian situation.

"At the moment, there is no pressure on our ICUs," he said.

There are 63 coronavirus patients in intensive care, with scope for 4400 beds to be made available immediately.

The national target is 7,200 ICU beds.

Many of the incidents that would often fill intensive care beds, such as car accidents or nightlife violence, have been curtailed by the restrictions on movements and venues.

Officials also hold grave concerns about an influx of caravans into regional Australia.

ST VINCENT'S HOSPITAL

Mayors are pleading with grey nomads and other holidaymakers to stay home and relieve pressure on towns during the pandemic.

Deputy Nationals leader David Littleproud, whose sprawling electorate covers 729,000 square kilometres of regional Queensland, said people must not seek refuge in country towns.

"Otherwise, these caravans could turn into the cruise ships of the outback," he told ABC Radio National.

Strict physical distancing measures are being enforced in NSW and Victoria, with police patrolling public places to make sure people are following the rules.

Harsh fines and jail time could be applied if people continue to break public health orders.

WEDNESDAY UPDATE: Coronavirus (#COVID19)

What's new:

- News and media

- Current situation

Read more: https://t.co/z9CfXFRtCG pic.twitter.com/pO8UaE0ZmK — Australian Government Department of Health (@healthgovau) April 1, 2020

Concerns continue to swirl about the availability of protective equipment including face masks.

Several million more masks have arrived in Australia in recent days but health authorities are cautious about running down supplies.

And Prof Kelly warned healthy people off using the precious resource.

"They shouldn't be using face masks in public because that would be a waste of face masks."

People in Australia must stay at least 1.5 metres away from others and gatherings are limited to two people unless you are with your family or household.

If you believe you may have contracted the virus, call your doctor (don’t visit) or contact the national Coronavirus Health Information Hotline on 1800 020 080.

If you are struggling to breathe or experiencing a medical emergency, call 000.

SBS is committed to informing Australia’s diverse communities about the latest COVID-19 developments. News and information is available in 63 languages at sbs.com.au/coronavirus