The President of the United States said the drug was previously approved as an anti-malaria treatment and for arthritis.

He told a press conference at the White House today that it had now also shown "tremendous promise" in treating Covid-19.

The drug, sold under the brand name Plaquenil, is used on the NHS to treat lupus and rheumatoid arthritis as well as malaria.

It's understood its effectiveness on coronavirus patients is also being tested in the UK, according to Sky News.

President Trump also said that another drug called Remdesivir had also been effective in treating the symptoms of the new illness.

The anti-viral drug was developed around a decade ago and was intended as a possible treatment for Ebola.

It's not yet been approved for coronavirus patients, but is being tested to see if it could relieve symptoms such as pneumonia, he said.

As the new illness has no cure, researchers around the world are desperately testing already in-use drugs for their effectiveness on combating Covid-19.

Scientists in China are also testing out flu, anti-HIV and arthritis drugs in experimental trials.

'Powerful drugs'

President Trump told reporters: "A drug called chloroquine, or hydroxychloroquine, is a common malaria drug. It’s also a drug used for strong arthritis.

"It's been around for a long time and it’s very powerful.

"The good thing is that because it's been around a long time we know that if things don't go as planned it's not going to kill anybody.

"When you go with a brand new drug you don’t know.

"But this has been used as a very powerful drug in different forms and it’s shown very, very encouraging results."

President Trump added that they would be making hydroxychloroquine available on prescription immediately, following its "tremendous promise" based on tests.

Promising therapies

President Trump also said there were promising therapies being produced by American biotech company Gilead Sciences, including a drug known as Remdesivir.

He said: "That’s a drug used for other purposes that's been out and had very good results but also has good results having to do with this virus.

"It’s very closed to being approved by the FDA and I can't tell you how much we appreciate them.

"Those are two that are out now, essentially approved for prescribed used.

"I think it’s very exciting and it could be a game-changer, or maybe not."

President Trump also called on the FDA to streamline its processes to speed up the development of therapies aimed at treating the coronavirus.

He said: "We have to remove every barrier."

Trials on potential coronavirus therapies are already in the works, and it was unclear how Trump's call for faster experimental testing process could further expedite an effective treatment.

FDA Commissioner Stephen Hahn said his agency was working quickly to examine all possibilities.

"In the short term, we're looking at drugs that are already approved for other indications," Hahn said.

The US leader is also expanding the nation's diagnostic testing capacity and deploying a Navy hospital ship to New York City, which is rapidly becoming an epicentre of the pandemic, and another such ship to the West Coast.

President Trump, who planned to visit the Federal Emergency Management Agency on Thursday, has also invoked rarely used emergency powers to marshal critical medical supplies against the coronavirus pandemic.

He signed an aid package which the Senate approved yesterday that will guarantee sick leave to workers who fall ill.