A limited emergency-use authorization for two antimalarial drugs touted as game-changers by President Donald Trump has been issued by the US Food and Drug Administration to treat coronavirus patients.

In a statement published Sunday, the US Department of Health and Human Services detailed recent donations of medicine to a national stockpile - including chloroquine and hydroxychloroquine, both being investigated as potential COVID-19 treatments.

It said the FDA had allowed them "to be distributed and prescribed by doctors to hospitalized teen and adult patients with COVID-19, as appropriate, when a clinical trial is not available or feasible."

Trump said last week that the two drugs could be a "gift from God," despite scientists warning against the dangers of overhyping unproven treatments.

Many researchers including Anthony Fauci, the United States' leading infectious disease expert, have urged the public to remain cautious until larger clinical trials validate smaller studies.

Two US medical bodies - the National Institutes of Health and the Biomedical Advanced Research and Development Authority - are currently working to plan such trials.

Some in the scientific community fear Trump's endorsement of the medicines could create shortages for patients who need them to treat lupus and rheumatoid arthritis, diseases for which they are approved.

The US has more than 140,000 novel coronavirus cases and 2,489 deaths, according to a tracker maintained by Johns Hopkins University.