It could be any warehouse in Australia. In fact, you may travel past it every day and not even know.

In multiple secret locations across Australia, about $100 million worth of medical supplies — including 20 million masks, antibiotics, vaccines and equipment such as basic hand sanitisers — is sitting on huge pallets wrapped in plastic, ready to be deployed.

It has been gradually accumulated over more than a decade in case of a bioterrorist attack, medical emergencies or pandemics.

It's known as the National Medical Stockpile (NMS).

And with coronavirus almost certain to be declared a pandemic, according to the Prime Minister, the stockpile is now, according to health authorities, set to become a critical element of the response to COVID-19 — its first major use in more than a decade.

How does it work?

States and territories request access to the stockpile — which is described by the Department of Health as a "strategic reserve of pharmaceuticals and personal protective equipment" — with final approval given by chief medical officer Brendan Murphy.

So far during the coronavirus epidemic, more than 1.4 million surgical masks have been handed to GPs, health workers, pharmacists, and government agencies dealing with "at-risk or high-risk individuals at the border".

Some stock is pre-positioned in the states and territories to ensure more rapid access to products in emergency situations, a Department of Health spokeswoman said.

The equipment is held in various nondescript warehouse locations across Australia, each one kept secret and under tight security because of concerns of terrorist attacks.

Last month, Health Minister Greg Hunt gave a rare insight into the warehouses, posting a photo on social media that showed hundreds of pallets of face masks stacked up over five levels.

Health Minister Greg Hunt touring one of the National Medical Stockpile warehouses in January. ( Twitter )

Since the coronavirus became a worldwide medical emergency, the Federal Government has been building up its supplies.

In January, Mr Hunt said they had 12 million facemasks. On Friday he revealed they had 20 million in storage.

"We are well stocked," he said on Friday.

"The priority is obviously in protecting the frontline clinicians and we will work with states and territories and primary health networks or whatever bodies to make sure that supplies are delivered to where they are needed.

"We do have strong supply chains. As part of our job, that is one of the items that was a specific Commonwealth action item."

There is no vaccine, but some drugs, such as antiviral medicine remdesivir, have been shown to help. However, Mr Hunt gave no indication that the Federal Government had been stocking up on remdesivir, or any other drugs.

The last high-profile use of the stockpile came during the 2009 swine flu pandemic. More than 900,000 courses of antivirals, valued at about $29 million, were deployed, with 2.1 million pieces of personal protective equipment also handed out.

Are there shortages of anything now?

Experts have raised concerns over gaps in the supply chain as Chinese factories remain closed because of the COVID-19 threat.

According to the World Health Organisation, China makes up about 20 per cent of the global output of active pharmaceutical ingredients.

However, some experts contest that figure and have gone as far as to describe China as having a "global choke-hold" on the chemical components that make up key pharmaceutical ingredients.

UNSW global biosecurity professor Raina MacIntyre said Australia "will see an impact" in supplies of some medical equipment and drugs in the general public.

"We have just-in-time economies where we don't have huge stockpiles that'll keep us going for months and months," she said.

"It is possible that patients will be affected by shortages, there might be very specific drugs that are made only in China."

"Although, China is gradually opening up factories and trying to get back to business as normal."

Australian Medical Association president Tony Bartone said there were "some reports" of certain medications and masks not being available.

"One of the key sources of supply is obviously the Chinese manufacturing sector and clearly they are confronting their own issues regarding logistical supply," he said.

A sign saying face masks have sold out at a pharmacy in Adelaide. ( Twitter: Colin Campbell )

On Friday, the president of the Royal Australian College of GPs, Harry Nespolon, said GPs urgently needed more protective equipment — including goggles and protective suits — so they could safely assess people who might have COVID-19.

Reports have already emerged of people panic-buying masks this week, following on from earlier panic-buying when the virus first came to light.

What else is in the National Medical Stockpile?

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 46 minutes 25 seconds 46 m How coronavirus sparked a global emergency.

Over the past 15 years, the total investment in the NMS has been about $900 million.

According to the Department of Health, about 80 per cent of the stockpile's value was tied up in pharmaceuticals, including antivirals such as Tamiflu and Relenza.

A 2014 auditor-general's report — one of the few publicly available documents online about the NMS — found as antivirals typically lasted for seven to 10 years, the "significant cost" of the NMS came because most drugs had to be thrown out.

It also holds a limited supply of "highly specialised drugs" which, in an emergency, may not be available elsewhere in the Australian pharmaceutical supply system.

In 2014, it said 14 per cent of items were related to chemical, biological, radiological and nuclear defence including "responses to anthrax and human influenza pandemics".