The US Food and Drug Administration (FDA) has approved emergency use of experimental anti-viral drug remdesivir to treat patients with COVID-19.

The authorisation was announced by President Donald Trump on Friday and granted to Gilead Sciences Inc, which will donate 1.5 million vials of the drug to help patients.

During a meeting in the Oval Office with Mr Trump, Gilead chief executive Daniel O'Day called the move a significant step towards easing the coronavirus crisis.

"We want to make sure nothing gets in the way of these patients getting the medicine, so we made a decision to donate about 1.5 million vials."

Mr O'Day said on Wednesday that the drug had helped improve outcomes for patients with COVID-19, and provided data suggesting it worked better when given earlier in the course of infection.

The closely watched drug has moved financial markets in recent weeks, following the release of several studies that painted a mixed picture of its effectiveness.

Interest in Gilead's drug has been high as there are currently no approved treatments or preventive vaccines for COVID-19.

Doctors are desperate for anything that might alter the course of the disease that attacks the lungs and can shut down other organs in extremely severe cases.

Mr Trump had previously spruiked hydroxychloroquine, despite infectious disease experts saying that the anti-malaria drug was unproven, even dangerous.

Gilead has defended prospects for remdesivir in helping fight the coronavirus pandemic against signs that it may also not provide a significant benefit.

A draft study abstract released inadvertently by the World Health Organisation (WHO) last week said remdesivir failed to improve patients' condition or reduce the pathogen's presence in the bloodstream.

The drug maker said the findings were inconclusive because the study was terminated early.

Remdesivir was previously tried as a treatment for Ebola, without success.

It is being tried against COVID-19 because it is designed to disable the mechanism by which certain viruses, including coronavirus, make copies of themselves and potentially overwhelm their hosts' immune system.

US Vice President Mike Pence said the 1.5 million vials would start being distributed to hospitals on Monday.

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Reuters/ABC