Superstar singer Madonna has been censored on Instagram for spreading false information about a supposed cure for COVID-19 after she shared clips from a video also re-tweeted by Donald Trump.

In her post to 15.4 million followers, Madonna claimed that a proven vaccine had been available for months but it was being kept secret "to let the rich get richer and the poor and sick get sicker."

She attached a video of US physician Stella Immanuel who praised hydroxychloroquine as a coronavirus cure. 

Clips of Immanuel's speech have spread rapidly on the internet recently, but hydroxychloroquine, an antimalarial drug, has not been proved effective against COVID-19.

"We've removed this video for making false claims about cures and prevention methods for COVID-19," a spokeswoman for Facebook, which owns Instagram, told AFP on Wednesday.