President Donald Trump has hailed authorisation of a coronavirus treatment that uses blood plasma from recovered patients, a day after accusing the US drug regulator of impeding the rollout of vaccines and therapeutics for political reasons.

The US Food and Drug Administration’s announcement of its “emergency use authorisation” of the treatment came on the eve of the Republican National Convention, where Mr Trump will be nominated to lead his party for four more years.

“This is what I’ve been looking to do for a long time,” Mr Trump told an unusually brief White House news conference on Sunday (local time). He took only three questions from journalists before leaving the briefing.

“Today I’m pleased to make a truly historic announcement in our battle against the China virus that will save countless lives.”

Explaining its decision, the FDA cited early evidence suggesting blood plasma could decrease mortality and improve the health of COVID patients if it was administered in the first three days of their hospitalisation.

The agency also said it had determined this was a safe approach in an analysis of 20,000 patients who received the treatment.

So far, 70,000 patients had been treated using blood plasma, the FDA said.

A day before the FDA’s announcement, Mr Trump tagged the agency’s Commissioner Stephen Hahn in a Twitter post in which he said, “The deep state, or whoever, over at the FDA is making it very difficult for drug companies to get people in order to test the vaccines and therapeutics.

Tweet from @realDonaldTrump

“Obviously, they are hoping to delay the answer until after November 3rd. Must focus on speed, and saving lives!”

Mr Trump is looking to boost his lagging poll numbers during this week’s Republican convention. Progress in treatments or an effective vaccine to gain control of the coronavirus would aid his re-election chances.

At least 5,686,377 cases of COVID-19 have been reported in the US, according to a Reuters tally, and more than 176,000 Americans have died.

US regulators provided emergency authorisation for Gilead Science Inc’s remdesivir as a therapeutic treatment for COVID-19 earlier in 2020.

The White House declined to comment on a separate report in the Financial Times that the administration is considering fast-tracking an experimental COVID-19 vaccine being developed by AstraZeneca Plc and Oxford University for use in the US before the November 3 presidential election.

-with AAP