Not everyone who wants a COVID-19 test will get one.

Australia doesn't have enough to go around, so doctors are being asked to limit tests to those most likely to test positive.

These include people who:

Have recently been overseas

Have recently been overseas Have been in contact with a known case

Have been in contact with a known case Have been hospitalised with pneumonia

Have been hospitalised with pneumonia Are frontline health workers

Are frontline health workers And, as of Friday, aged care workers

If you're worried you might have COVID-19, Queensland Health has created a quiz you can take (regardless of which state you're in) to find out what you should do.

But don't be surprised if the advice changes regularly.

Australia's chief medical officer Professor Brendan Murphy said: "As this pandemic develops we will be continually reviewing the testing criteria."

How do they test for coronavirus?

The test involves looking for evidence of the virus in respiratory samples, which can include swabs from the back of the nose and throat, or fluid from the lungs.

The Public Health Laboratory Network (a group of Australian and New Zealand public health microbiology experts) released guidelines for health workers on how to conduct a COVID-19 test safely.

It gives you some idea of what to expect.

It says the person taking the test should be wearing gloves, gowns, eye protection and a surgical mask.

They should stand slightly to the side of the patient in case the patient coughs or sneezes.

If the patient has severe symptoms like fever, breathing difficulty, pneumonia or coughing fits, the sample should ideally be collected in a negative pressure room in a hospital.

But that's not always possible.

A doctor takes a swab from a woman at a fever clinic in China. ( AP: Chinatopix )

To collect the test a swab will be moved along the tonsillar beds and the back of the throat, avoiding the tongue.

In order to conserve swabs, that same swab should then be used in the nose.

It should be gently inserted along the floor of the nasal cavity and rotated for 10 to 15 seconds, withdrawn and then repeated on the other nostril.

Lower respiratory tract samples may also be taken, in which case the patient should rinse their mouth with water and then cough phlegm into a sterile, screw-top container.

These lower respiratory tract specimens contain the highest viral loads, so should be used for SARS-CoV-2 testing where possible.

You may also have a blood test.

What happens to the samples

Not only is there a shortage of swabs and reagent test kits for COVID-19, there's also a backlog at pathology labs.

New South Wales chief health officer Dr Kerry Chant said: "We are testing almost 24/7."

Originally only the biggest laboratories conducted the testing, but, increasingly, more private and smaller pathology laboratories are being accredited and coming on board.

Victoria's chief health officer Dr Brett Sutton said the Victorian Infectious Diseases Reference Laboratory was doing more than 1,000 tests per day.

"The test takes about three hours to run through in the lab," he told ABC Radio Melbourne on Monday.

"There are now lots of little pathology laboratories popping up and starting to do them locally and they're doing a few hundred per day and again, they probably run through in a couple of hours on the PCR machines."

The polymerase chain reaction (PCR) is a technique which amplifies genetic material in order to identify if the genetic material of the virus is present.

Where to get tested for coronavirus

Samples for testing can be taken by GPs, public hospitals and at some private pathology sites.

Some of these will involve drive-through testing, others won't.

You will need to call ahead to speak to your GP about testing.

Major COVID-19 clinics at public hospital may not require you to phone ahead.

Here's where to find out specific information for your state:

How long does a COVID-19 test take?

Some medical professionals in Australia have been testing people in their cars. ( ABC News: Haidarr Jones )

According to the Federal Health Department, it may take a few days for the test results to come back.

The NSW Health Department says the wait can be up to two days.

If you have serious symptoms you will be kept in hospital and isolated from other patients to prevent the virus spreading.

If your doctor says you are well enough to go home while you wait for your test results, as will be the case for most people, you should:

self-isolate at home and not attend work or school

self-isolate at home and not attend work or school protect yourself and others

protect yourself and others notify a doctor if your condition deteriorates and tell them you're waiting on test results for COVID-19

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What happens if you test positive

Bridget Wilkins was one of the first cases of coronavirus diagnosed in Australia.

She came back from overseas and was surprised when her GP suggested she get tested.

When the test came back positive Ms Wilkins was taken to hospital to help prevent the spread of the virus.

"It felt like a bit of a con, to be honest, to walk into hospital feeling fairly healthy, yet everyone's in hazmat suits," she said.

Bridget Wilkins with a hospital worker during her isolation. ( Supplied: Bridget Wilkins )

Initially her symptoms were not severe; a sore throat, a headache and "a little bit of fever".

But her condition deteriorated around day eight to include intense headaches and chest pain.

She ended up spending 13 days in isolation in a Brisbane hospital.

Actor Tom Hanks and musician Thelma Plum also spent time in hospital after testing positive.

Plum was diagnosed on Monday, and was being managed by the Brisbane Metro North Public Health Unit.

"They're taking very good care of me," Plum wrote on Instagram.

"At this time the Dr wants to keep me here until at least Friday, but the rules around being released are constantly changing."