SYDNEY (REUTERS) - Australia's national science agency said on Thursday (April 2) it has begun the first stage of testing potential vaccines for Covid-19 as it joins a global race to halt the coronavirus pandemic.

Pre-clinical testing by the Commonwealth Scientific and Industrial Research Organisation (Csiro), comprising injecting ferrets with two potential vaccines, was under way at its high-containment biosecurity facility near Melbourne.

The first phase of testing would take around three months, Csiro director of health Rob Grenfell told Reuters, adding that any resulting vaccine would not be available to the public before late next year.

"We're still sticking to the optimistic 18 months for delivery of vaccine to the general consumers," Dr Grenfell said from Melbourne in an interview over Skype. "Now this, of course, may change. There's a lot of technical challenges that we're having to go through."

Dr Grenfell said scientists were working at a "remarkable" pace, reaching the pre-clinical testing stage in about eight weeks, a process that usually takes up to two years.

"So, this is the speed that's going on at the moment."

More than 850,000 people have been infected with the novel coronavirus across 207 countries and territories, killing more than 42,000. Australia has reported around 5,200 cases and 24 deaths.

Dr Grenfell said he expected human trials of one of the two vaccine candidates being tested to begin later this month or early next month.

Csiro said its testing would cover both efficacy and evaluating the best way to administer the vaccine for better protection, including an intra-muscular injection and a nasal spray.

Csiro was the first research organisation outside of China to successfully develop a lab-grown version of the virus to enable pre-clinical studies on Covid-19.

In February, it confirmed that ferrets reacted to the coronavirus as they shared with humans a particular receptor on their respiratory cells that the virus binds itself to.

"If we can stop that virus binding to the ferret receptors in the respiratory system, there's a very good chance it (vaccine) will work in humans," Dr Grenfell said.

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Moderna Inc is the closest publicly known facility to human testing, announcing plans to start a trial in Seattle last month.

The US government has cut deals with both Moderna and Johnson & Johnson, and is in talks with at least two other companies, to produce massive quantities of vaccines.

Israel has begun testing a Covid-19 vaccine prototype on rodents at its bio-chemical defence laboratory, a source told Reuters on Tuesday.

In Australia, thousands of healthcare workers last week entered a trial to see if a century-old vaccine for tuberculosis can fight off the novel coronavirus.