Americans are being urged to "resist confusing reopening with returning to normalcy" and their president is being pressed to acknowledge that COVID-19 is a "major problem", as the death toll from the pandemic exceeded 130,000 on Monday.

Two days after US President Donald Trump asserted without providing data that 99 percent of US novel coronavirus cases were "totally harmless", three leading US health organizations issued an open letter, asking people to help stop "the worst public health crisis in generations" by wearing masks, social distancing and washing hands.

"COVID-19 is not behind us and we must resist confusing reopening with returning to normalcy," officials of the American Medical Association, American Nurses Association and American Hospital Association said in the plea.

"Doing so will escalate this crisis and result in more suffering and death," they said.

The health groups said that in the weeks since states began reopening, some of the steps taken early on that were critical to the progress in declined infection and deaths "were too quickly abandoned".

As a result, "we are now watching in real-time as a dramatic uptick in COVID-19 cases is erasing our hard-won gains".

"We are not powerless in this public health crisis, and we can defeat it in the same way we defeated previous threats to public health — by allowing science and evidence to shape our decisions and inform our actions," they said.

Confirmed cases are on the rise in 41 out of 50 states plus the District of Columbia, and the percentage of tests coming back positive for the virus is increasing in 39 states, The Associated Press reported Monday.

In California, new coronavirus cases soared over the July Fourth weekend. At least 11,500 residents tested positive in the past 24 hours, according to state records.

New York Governor Andrew Cuomo, whose state is cautiously proceeding with a phased reopening, said, "The virus goes up, stock market goes down and now the states are saying we have to close again."

At a news briefing Monday, the Democratic governor said the Republican president was "enabling" the virus if he failed to address the severity of the situation.

"Don't be a co-conspirator of COVID, do one simple thing: acknowledge to the American people that COVID exists; it is a major problem; it's going to continue until we admit it and each of us stands up to do our part," Cuomo said.

He again urged the president wear a mask, saying that New York initiated a mask policy on April 15, first state in the nation to do so, which has made a difference.

Trump has averted to wearing a mask in public but said last week he would use one "in a tight situation with people".

Jim Justice, the Republican governor of West Virginia, which has seen the number of confirmed COVID-19 cases rise by 30 percent over the past two weeks, issued a mandatory mask order Monday, requiring everyone age 9 and above to wear face coverings inside buildings when social distancing isn't possible.

White House chief of staff Mark Meadows said Monday that a national mandate requiring Americans to wear masks was "not in order" and the decision to require masks is a "state-to-state issue".