Restaurants and bars also were singled out for a weekend crackdown on coronavirus enforcement in California, where hospitalisations for the highly contagious respiratory virus have jumped 50 per cent over the past two weeks.

For an eighth straight day, Texas registered an all-time high in the number of people hospitalised with COVID-19 at any one moment, up more than 500 admissions from the day before to nearly 8700.

California, Texas and Florida are all among two dozen states reporting high infection rates as a percentage of diagnostic tests conducted over the past week, an alarming sign of a virus still spreading largely unchecked throughout much of the country.

The Miami-Dade County emergency restaurant closure was ordered on Monday by Mayor Carlos Gimenez, the top official in a metropolitan area that has reported some 48,000 COVID-19 infections to date among its 2.8 million residents.

The move, just weeks after eateries began welcoming customers back, left struggling restaurateurs even more worried about the survival of their businesses.

Michael Beltran, chef-partner at Ariete Hospitality Group, which owns a handful of other popular Miami restaurants including Taurus, was struggling to come to terms with having to tell most of his 80 employees that they would again be unemployed.

"From what they told me, I did the proper things (to reopen), and now we're at this point," Beltran said.

Florida, one of the last states to impose mandatory workplace closures and among the first to try relaxing them, reported more than 6000 new cases on Monday.

COVID-19 infections are on the rise in 39 states, according to a Reuters analysis of cases over the past two weeks, with the country as a whole averaging some 50,000 new cases nearly every 24 hours in recent days.

More states are also reporting a troubling increase in the percentage of COVID-19 diagnostic tests that come back positive - a key indicator of community spread that experts refer to as the rate of "positivity."

Several states were averaging double-digit rates and climbing, including Arizona at 26 per cent, Florida at 19 per cent and Mississippi at 17 per cent.

California's positivity rate has also risen over the past two weeks. But Governor Gavin Newsom on Monday cited a 50 per cent two-week spike in hospitalisations as an impetus for beefed-up enforcement actions during the Fourth of July holiday.

He said state regulators visited nearly 6000 bars and restaurants over the weekend to ensure compliance with rules barring indoor seating, or the reopening of any establishment that normally serves alcohol without food.

The nationwide loss of life from COVID-19 surpassed 130,000 on Monday, and the US Centres for Disease Control and Prevention forecast that the death toll could reach 160,000 later this month.

The disquieting surge in new cases has prompted many local leaders to slow down or roll back business reopenings in hopes of curbing infection rates that have started to overwhelm hospitals in some areas.

"We can tamp down the spread if everyone follows the rules, wears masks and stays at least six feet apart from others," Gimenez said in a statement announcing his emergency order, which also closed ballrooms, banquet halls, party venues, fitness centres and short-term housing rentals.

Colleges and universities have likewise been forced to adjust their reopening plans.

As the cumulative US case total nears 3 million - about a quarter of all known infections worldwide - scrutiny of President Donald Trump's handling of the crisis has intensified.

Trump, who has suggested scaling back COVID-19 testing to keep the number of reported cases in check, said in a speech on Saturday that 99 per cent of US coronavirus infections were "totally harmless," but offered no evidence to support his assertion.

Australian Associated Press