WASHINGTON (REUTERS) - US President Donald Trump said he underwent a second coronavirus test on Thursday (April 2), using a rapid diagnostic that produced a result in less than 15 minutes, and it determined that he has not been infected.

"I think I took it really out of curiosity to see how quickly it worked," said Mr Trump, who also tested negative last month after coming into contact with a Brazilian official who later tested positive for the coronavirus.

At his daily White House news briefing, Mr Trump announced plans for the US military and federal personnel to operate a makeshift hospital set up in the Javits Centre convention centre in New York to help the city grapple with a flood of patients.

New York has become the epicentre of the US epidemic with more than 47,000 confirmed cases in the city.

White House senior adviser Jared Kushner, a member of the coronavirus task force, said the government will send to the New York public hospital system a supply of N-95 protective masks to help medical workers get through the next month.

Mr Trump, who had initially played down the threat from the virus, made use of the Korean War-era Defence Production Act to try to order companies to produce hospital ventilators essential in keeping alive patients hit hard by the Covid-19 respiratory illness caused by the coronavirus.

He said he also used the law to get General Motors Co to produce more N-95 masks.

"We have over 100,000 (ventilators) being built right now or soon to be started," Mr Trump said.

He said he had just spoken with General Motors Chief Executive Mary Barra, who told him they will soon be ready to start production of ventilators.

Related Story Coronavirus explainers: What you should know to protect yourself

Related Story Coronavirus visual guide: Interactive graphics on the pandemic

Mr Trump's physician, Sean Conley, said in a letter released by the White House that Mr Trump was tested with a new, rapid point-of-contact test and the result came back in 15 minutes.

"He is healthy and without symptoms," Dr Conley said.