Amid a growing number of infections nationwide, President Donald Trump downplayed the threat of the novel coronavirus, even as a top Trump administration health official said Sunday it was not clear whether it will be safe to hold the Republican National Convention (RNC) in Jacksonville, Florida, next month.

The state of Florida reported 9,999 new infections Sunday afternoon, bringing the state's total number of cases to 200,111, according to the Florida Department of Health website.

Florida reported eight new deaths Sunday. There have been 3,731 total deaths in the state.

This news comes a day after state officials announced 11,445 new daily coronavirus cases in Florida — which was then an all-time high.

Speaking on CNN's State of the Union, US Food and Drug Administration Commissioner Stephen Hahn refused to confirm Trump's claim Saturday that "99 percent" of coronavirus cases were "totally harmless", calling the COVID-19 situation a "serious problem."

With record numbers of people testing positive for the virus in Jacksonville and across Florida, Hahn was asked if it would be safe to hold the typically large political gathering in just seven weeks.

"I think it's too early to tell," Hahn told CNN. "We will have to see how this unfolds in Florida and elsewhere around the country."

Hahn, a member of the White House Coronavirus Task Force, was asked to comment on his boss' statement, which was made during a July Fourth speech at the White House.

"I'm not going to get into who is right and who is wrong," Hahn continued. "It's a serious problem that we have. We have seen the surge in cases. We must do something to stem the tide."

The Republican Party moved most of the RNC's activities to Jacksonville from Charlotte, North Carolina, last month after a battle over coronavirus safety concerns with that state's Democratic governor.

Trump enjoys seeing large crowds at his rallies, but he has not embraced masks or social distancing measures at campaign events held since the country began reopening from the coronavirus shutdown, though on Wednesday he endorsed mask wearing despite resisting wearing one himself in public.

"I'm all for masks. I think masks are good," Trump told Fox Business News.

Coronavirus cases rose in 39 states, casting a shadow over the nation's Independence Day celebrations. Ahead of the July Fourth weekend, public health experts warned that holiday parties could cause further spikes in infections that could overwhelm hospitals.

In the first four days of July alone, 15 states have reported record increases in new cases of COVID-19. There are at least 2.8 million cases of coronavirus in the US, and at least 129,000 Americans have died so far, according to data from Johns Hopkins University.

Florida's cases have risen by more than 10,000 for three out of the last four days. Cases are also soaring in Arizona, California and Texas and trending upward in Midwestern states that once had infections declining such as Iowa, Ohio and Michigan, according to a Reuters analysis of how much cases rose in the past two weeks compared with the prior two weeks.

"We opened way too early in Arizona," said Phoenix Mayor Kate Gallego on ABC's This Week on Sunday. She said the city was in a "crisis related to testing", with people waiting in eight-hour lines in their cars to find out if they were infected.

"It's really, really difficult. I've been spending time begging everyone from Walgreens to open up testing, out-of-state testing companies to come in because it's awful to see people waiting in a car, while you're feeling sick, people were running out of gas, and this is as many months in," Gallego said.

In Texas, the number of COVID-19 patients currently hospitalized rose to a record 7,890 on Saturday compared with 3,247 two weeks ago. The Democratic mayor of Austin, Texas, warned during an interview with CNN that his city's hospitals could reach capacity in two weeks and run out of intensive care unit (ICU) beds in 10 days. In Arizona, about 90 percent of ICU beds are full.

Reuters contributed to this story.