Canadian health authorities have issued a warning against the use of anti-malarial drugs chloroquine and hydroxychloroquine to treat coronavirus infections or prevent reinfections.

"Chloroquine and hydroxychloroquine can have serious side effects. These drugs should be used only under the supervision of a physician," Canada's public health agency said in a note posted Saturday on its website.

"Health Canada is concerned that some people may be directly buying and using chloroquine or hydroxychloroquine to prevent or treat COVID-19," it said, noting they can cause "serious heart rhythm problems."

The European Medicines Agency and the US Food and Drug Administration this week issued similar warnings about the drugs, whose promise as a coronavirus treatment has been touted by US President Donald Trump.

Health Canada said chloroquine and hydroxychloroquine were approved to treat malaria and certain autoimmune diseases like lupus and rheumatoid arthritis but were known to potentially cause liver or kidney problems, low blood sugar and nervous system problems.

"The effects on heart rhythm... in the most serious cases, may be fatal," it said.