US President Donald Trump said Monday that he has been taking the malaria and lupus drug hydroxychloroquine, which is unproven for fighting COVID-19, to lessen symptoms if he gets the novel coronavirus.

In the weeks before telling reporters he was taking the drug, Trump has touted it as a potential cure for COVID-19, even though the Food and Drug Administration (FDA) cautioned last month that it could cause significant side effects in some patients, including heart rhythm problems, and should be used only on hospitalized patients or as part of clinical trials.

Trump made the revelation during a roundtable with restaurant executives at the White House.

He then told reporters that he has been taking hydroxychloroquine and a zinc supplement daily "for about a week and a half now and I'm still here, I'm still here".

Trump said his doctor didn't recommend the drug to him but that he requested it from the White House physician.

"I started taking it, because I think it's good. I've heard a lot of good stories," he said, suggesting that many medical workers were also taking the drug.

"You'd be surprised at how many people are taking it, especially the front-line workers before you catch it … many, many are taking it," he said.

The president said he doesn't know if it works, but "if it doesn't, you're not going to get sick and die", he added, seeming to brush aside FDA warnings.

Nearly 1.5 million people in the US have tested positive for the coronavirus and more than 90,000 of them have died, according to data from Johns Hopkins University.

On Monday, more states lifted restrictions, including Michigan, where Governor Gretchen Whitmer has stayed firm with one of the nation's toughest lockdowns despite protests from Republican opponents and armed protests at the statehouse.

Whitmer signed an order that will allow businesses and restaurants in northern Michigan to reopen by the Memorial Day weekend. The order affects the sparsely populated Upper Peninsula and 17 counties in the tourism-heavy northern tip of the Lower Peninsula.

New York, California and Massachusetts on Monday also eased restrictions, and Trump continued to his push for a wider reopening: "REOPEN OUR COUNTRY!" Trump wrote in a Twitter post Monday and "TRANSITION TO GREATNESS".

Most states reported a drop in new cases of the coronavirus for the week ended May 17, with only 13 states seeing a rise in infections compared with the previous week, according to Reuters. Tennessee had the biggest weekly increase at 33 percent.

New York Governor Andrew Cuomo said the western corner of the state, which includes Niagara Falls, would become the sixth of New York's 10 regions to start reopening Tuesday.

New York, which has the most deaths of any state — 27,400 — is showing more signs of containing the spread. The three-day rolling average of hospitalizations is declining, and the number of fatalities dropped to 106 on Sunday versus 139 on Saturday.

New York City Mayor Bill de Blasio said Monday that the city may meet the thresholds set by the state to reopen in the first half of June.

In the San Francisco Bay Area, health directors in five counties said manufacturing and retail with curbside pickup and warehouse distribution could reopen.

Manufacturing facilities and construction sites in Massachusetts were allowed to resume operations Monday as the state began its gradual reopening.

In Washington, Health and Human Services Secretary Alex Azar on Monday rebuked Peter Navarro, the president's trade adviser, for blaming the Centers for Disease Control and Prevention (CDC) for early problems with coronavirus testing. He called Navarro's comments "inaccurate and inappropriate".

Navarro said Sunday on NBC's Meet the Press that the CDC "really let down the country" and set back efforts to combat the virus by mismanaging the rollout of the first diagnostic test.

In an interview with Fox News, Azar, whose department oversees the CDC, said the CDC's initial test was problematic, but he contended it didn't set back the coronavirus response.