Florida reported a record increase of more than 15,000 new cases of Covid-19 in 24 hours on Sunday, a day after Walt Disney World in Orlando reopened and anti-mask activists held a rally at a nearby restaurant.

If Florida were a country, it would rank fourth in the world for the most new cases in a day behind the United States, Brazil and India, according to a Reuters analysis.

Florida's daily increases in cases have already surpassed the highest daily tally reported by any European country during the height of the pandemic.

Florida has also broken New York state's record of 12,847 new cases on April 10 when it was the epicentre of the US outbreak.

Walt Disney Co welcomed a limited number of guests to its two most popular parks in Orlando on Saturday with a host of safety measures including masks and temperature checks.

Coronavirus infections are rising in about 40 states, according to a Reuters analysis of cases for the past two weeks compared with the prior two weeks.

Nationally, the United States has broken global records by registering about 60,000 new cases a day for the last four days in a row, according to a Reuters tally.

Hospitalisations and positive test rates are also rising in states at the centre of the outbreak — Arizona, California, Florida and Texas.

Health officials have pleaded with the public to wear masks to limit the spread of the virus, but the issue has become politically divisive in the United States unlike many other countries that have seen far lower rates of infection and death.

Seven months into the pandemic, US President Donald Trump wore a mask for the first time in public when he visited a Washington DC-area military medical centre on Saturday. Trump had previously refused to wear a mask in public or ask Americans to wear face coverings, saying it was a personal choice.

Many Americans still refuse to wear a mask, which health experts say help stop transmission of the virus that has killed more than 134,000 Americans.

Anti-mask activists organised a protest on Saturday at a grilled cheese restaurant and bar in Windermere, Florida, which is in Orange County about 19 kilometres from Walt Disney World.

The restaurant has become a focal point of tension after owner Carrie Hudson said she was not requiring customers to wear masks. County officials have mandated the use of masks in public since June 20.

During Saturday's protest, no customers wore face coverings inside the restaurant. Agents from the state's Division of Alcoholic Beverages and Tobacco arrived during the rally and served Hudson with a warning, according to a video.

“This is a virus that is very well contained,” said one of the demonstrators, anti-mask activist Tara Hill.

“Everyone is responsible for their own health care decisions [...] We want our choices respected as well.”

Florida has posted record levels of coronavirus infections, with over 10,000 new cases five times in the last 10 days.

In addition, more than four dozen hospitals in Florida reported that their intensive care units are full due to a surge in Covid-19 patients.