MIAMI (REUTERS) - Florida and Texas, two states that have emerged as the latest hot spots of the US coronavirus outbreak, both reported new single-day record increases in confirmed Covid-19 cases on Saturday (July 4) - with nearly 20,000 additional infections combined.

For a sixth straight day, Texas also registered an all-time high in the number of people hospitalised with the highly contagious respiratory illness - 7,890 patients after 238 new admissions over the past 24 hours.

By comparison, New York state - the US epicentre of the outbreak months ago, reported just 844 hospitalisations on Saturday, far below the nearly 19,000 hospital beds occupied by Covid-19 patients at the peak of its coronavirus crisis.

During the first four days of July alone, a total of 14 states have posted daily record increases in the number of individuals testing positive for Covid-19, the disease caused by the novel coronavirus that has killed nearly 130,000 Americans.

And in a further sign the virus is spreading, at least 18 states, including the three most highly populated - California, Texas and Florida - have posted ominous rates of infection as a percentage of diagnostic tests over the past two weeks.

The recent surge, most pronounced in Southern and Western states that were among the latest to impose mandatory business restrictions at the outset of the pandemic and the first to relax them, has alarmed public health officials ahead of weekend July Fourth holiday celebrations.

The majority of Independence Day fireworks displays across the country have been cancelled, as state and local authorities urged Americans to avoid large crowds, practice safe social distancing and wear face coverings while out in public.

Not everyone heeded those warnings. Video images posted on social media showed tightly packed crowds of swimsuit-clad young adults dancing to rock music in the shallows of Diamond Lake, a boating and recreational site in Cassopolis, Michigan.

Beaches were closed across much of Southern California and South Florida through the holiday weekend due to the coronavirus resurgence. But the seaside resort of Ocean City, Maryland, was open to the public, as were beaches along Alabama's Gulf Coast and Clearwater, Florida.

Florida's confirmed coronavirus cases rose by a record 11,458 on Saturday, the state's health department said, marking the second time in three days that its caseload jumped by more than 10,000 in 24 hours.

The latest figure in Florida surpassed the highest daily tally reported by any European county during the height of the coronavirus outbreak there.

In Texas, meanwhile, the number of new cases rose by a record 8,258 on Saturday, the state health department reported.

North Carolina, South Carolina, Tennessee, Alaska, Missouri, Idaho and Alabama all registered new daily highs on Friday.

Despite the rising number of cases, the average daily US death toll has gradually declined in recent weeks, reflecting the growing proportion of positive tests among younger, healthier people less prone to severe illness when infected.

Still, a growing number of states are reporting a troubling upward trend in the percentage of diagnostic tests that come back positive - a key indicator of community spread that experts refer to as the positivity rate.

The World Health Organisation considers positivity rates above 5 per cent to be concerning, and widely watched data from Johns Hopkins University shows at least 18 states with average rates over the past two weeks exceeding that level and climbing.

Eleven states averaged double-digit rates over the past seven days - Arizona (26 per cent), Florida (18 per cent), Nevada (16 per cent), South Carolina (15 per cent), Alabama (15 per cent), Texas (14.5 per cent), Mississippi (14 per cent), Georgia (13 per cent), Idaho (11 per cent), Kansas (10 per cent) and Utah (10 per cent).

That was up from four states with double-digit rates two weeks ago. Even in California, which led the nation with statewide workplace closures and stay-at-home orders issued on March 19, the positivity rate has crept up to an average of 7 per cent over the past week.

Against that backdrop, Miami-Dade County Mayor Carlos Gimenez imposed an indefinite nightly curfew starting Friday and halted the reopenings of entertainment venues such as casinos and strip clubs.

Arkansas on Friday joined a push towards mandating mask-wearing in public, with Governor Asa Hutchinson authorised the state's cities and towns to enact a "model ordinance" requiring the wearing of face coverings if they choose to do so.

The move came a day after Texas Governor Greg Abbott ordered that face masks be worn in most public places, reversing his stance following an alarming rise in infections.

President Donald Trump has repeatedly sought to minimise the jump in confirmed cases as a function of greater testing and again this week predicted that the virus would "disappear."

In a July Fourth speech at the White House, Trump claimed without evidence that 99 per cent of cases in the United States were "totally harmless."