Nancy Pelosi has spoken of her alarm and concern after Donald Trump revealed he has been taking an anti-malaria drug to prevent coronavirus.

The Speaker of the US House was among many who criticised the President after he announced he takes hydroxychloroquine every day, with medical experts labelling it ‘dangerous’.

The speaker of the House of Representatives told CNN:  “He’s our president, and I would rather he not be taking something that has not been approved by the scientists, especially in his age group and his, shall we say, weight group ... morbidly obese, they say."

Trump, who is 73, recorded a body mass index of 30.4 at his last medical check up. 

Individuals need to have a BMI of 40 to be considered to be ‘severely’ obese, according to the Centers for Disease Control and Prevention.

Chuck Schumer, the Democratic leader of the Senate, told MSNBC Trump was reckless to say he was taking the drug.

“Maybe he’s really not taking it because the president lies about things characteristically," he said.

“I don’t know whether he is taking it or not. I know him saying he is taking it, whether he is or not, is reckless, reckless, reckless.”

Moments after the president told reporters that he began taking the medication about a week and a half ago, host of the Trump-friendly Fox News, Neil Cavuto, issued an urgent warning, telling the channel’s largely elderly audience that there is no evidence the drug can ward off Covid-19, but it can cause potentially fatal irregular heartbeats.

Cavuto said: “If you are in a risky population here and you are taking this as a preventative treatment to ward off the virus, or in a worst case scenario, you are dealing with the virus, and you are in this vulnerable population, it will kill you. I cannot stress enough: this will kill you.”

His warning was echoed by Dr Bob Lahita, who told Cavuto that doctors at St Joseph University Hospital, where he is chairman of medicine, had seen ‘absolutely no effect’ on Covid-19 from hydroxychloroquine. 

Lahita also explained that the drug needs to be used only under close medical supervision, since it can cause ‘a fatal arrhythmia, which means an irregular heart rhythm, which will cause your death — your death will be instantaneous’.

There was also an extraordinary reaction in China, where representatives of the state media said Trump was using ‘witchcraft’.

Editor of the state-supported Global Times, Hu Xijin, tweeted: “President Trump is leading the US's struggle against pandemic with witchcraft, and as a result, more than 90,000 people have died. If it were in China, the White House would have been burned down by angry people.”

Trump has been peddling the drug as a prevention for the virus for a number of weeks despite medical advisers close to him saying there is no proof it works.

And other prominent doctors have warned people not to follow in Trump's footsteps. 

President of the American Medical Association, Dr Patrice Harris, said: “There is no evidence that hydroxychloroquine is effective for the treatment or the prevention of Covid-19. The results to date are not promising.”