WASHINGTON (REUTERS, AFP) - President Donald Trump said on Friday (March 13) that coronavirus testing in the United States will soon happen on a large scale, but did not provide any details on how that would be accomplished.

"The changes have been made and testing will soon happen on a very large scale basis. All Red Tape has been cut, ready to go!" he wrote in a tweet.

Trump also criticised the Centers for Disease Control and Prevention (CDC), one of the US organisations leading the fight against the deadly infection, for having a testing system that he said would "always be inadequate and slow for a large-scale pandemic".

Mr Trump did not elaborate on why the system was inadequate, but on Thursday, the top US official on infectious diseases, Dr Anthony Fauci, said people cannot get tests easily and the US testing system "is not really geared to what we need right now".

US officials and lawmakers are struggling to get a sense of how many people in the country have contracted the virus, which they attribute to low testing rates.

As of Friday, there were more than 1,700 cases and 40 deaths in the US, according to a tracker maintained by Johns Hopkins University.

Between 70 million and 150 million people in the United States could eventually be infected, according to a projection shared with Congress, a lawmaker said on Thursday.

Congressman Rashida Tlaib made the remarks during a hearing of the House of Representatives with members of the President's coronavirus task force, confirming earlier reports by US media outlets, including Axios and NBC News.

"Congress' attending physician told the Senate that he expects between 70 (million) to 150 million people to eventually contract the coronavirus in the United States," Ms Tlaib said.

Axios had reported that Dr Brian Monahan conveyed the projection to Senate senior staff on Tuesday, telling them they should prepare for the worst and offering advice on how to remain healthy.

The upper end of the projection is about 46 per cent of the US population of 327 million people.

By comparison, German Chancellor Angela Merkel warned this week that up to 70 per cent of her country's population could get the virus.