US health officials say they have successfully treated an American coronavirus patient with an experimental drug.

Remdesivir was made by American pharmaceutical company Gilead Sciences, and was used on a 35-year-old man in Snohomish County, Washington state, the Washington Post reported.

While the man recovered from coronavirus, Giliead says a single case can't be used to determine the drug's effectiveness on the disease.

The drug showed promise in laboratory tests against other viruses, including severe acute respiratory syndrome (SARS) and Middle East respiratory syndrome (MERS).

But a Gilead spokesperson told the New York Times that while it's exciting, the drug has only been used in a small number of patients with coronavirus.

"I think starting a clinical trial is essential for determining if this drug will work [against the coronavirus,"

"We do not have an appropriately robust understanding of the effect of this drug to warrant broad use at this time," Ryan McKeel said.

Two clinical trials will take place in Wuhan, where 500 patients will receive the drug and a comparison group will get a placebo.

One trial involves people who are severely ill with the virus with symptoms that include needing oxygen. The other trial will include patients who are hospitalised but not as sick.

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McKeel said the drug will be given intravenously for 10 days, and patients will be assessed 28 days after treatment to see if there are any differences when compared with the placebo group.

Gilead stockpiled Remdesivir to use against the Ebola outbreak in 2014, but it failed the clinical trial.

However, it's hoped that the drug will be one that works across multiple bugs.

Assistant professor of epidemiology at the University of North Carolina at Chapel Hill Timothy Sheahan told the Washington Post it may be able to work for multiple viruses instead of a new drug needing to be developed for each emerging virus.

"I think starting a clinical trial is essential for determining if this drug will work [against the coronavirus," Sheahan said.

Gilead says they're providing the drug to the Chinese researchers at no cost.