TAMPA, Fla. (WFLA/NBC) – There is growing concern about rising COVID-19 cases in Florida as it prepares to reopen schools next month.

The state recorded a record 15,300 new COVID-19 cases on Sunday. That’s more than all the new cases in Europe combined, Dr. Ashish Jha, director of the Harvard Global Health Institute told the Today Show’s Savannah Guthrie on Monday.

There were 15,284 new cases in Europe Sunday, data shows.

It’s the largest single-day tally for any state since the outbreak began. Florida broke California’s record of daily positive cases — 11,694, set on Wednesday. New York had the previous record of daily positive cases in April —11,571.

“The situation in Florida is pretty worrisome. There were more cases yesterday in Florida than all of Europe yesterday, and this is obviously a situation that is getting worse,” Jha said.

The death toll rose by 514 last week, an average of 73 deaths per day. More than 4,300 people have died in Florida since the pandemic began.

Florida Governor Ron DeSantis has attributed the spike in cases to increased testing and outbreaks among young adults who are not social distancing.

“If you look at that 25 to 34 age group, that is now by far the leading age group for positive tests,” DeSantis said last week.

Florida doubled testing over the last month and is now administering about 50,000 tests per day.

“Look, there has been a surge in testing, but what we’ve seen in Florida is a big increase in hospitalizations. That can’t be explained by testing. And now we’re seeing a big increase in deaths, and obviously, that can’t be explained by testing,” Jha said. “The fact that it is among a slightly younger population is helpful, but we are still seeing many of them get sick and many of them die.”

Jha said that new data from states like Texas indicates older people are starting to get infected again.

“Part because old people and young people co-mingle. They live with each other. So the idea that it could stay just among young people is probably unrealistic,” Jha said.

Jha blamed the spike in cases on Florida opening too early and too aggressively, and Florida leaders being too slow to react.

“I think the biggest problem recently is that they’ve been too slow to react. Still don’t have a statewide mandate for masks. There are a lot of other things that I think they still should be doing, and I don’t think Florida has been as aggressive as it needs to be,” Jha said.

Despite the recent surge in cases, Florida is still on track to reopen schools in August. Education Secretary Betsy DeVos said there’s nothing in the data that suggests that kids being in school is in any way dangerous. Jha called her comments “cavalier.”

“There is no question in my mind that kids are less likely to get sick, and there is pretty good evidence that they’re less likely to spread the disease in adults, but that’s really not the question,” Jha said. “The question is, in a hotspot like Arizona or Texas or Florida or probably about a dozen states, if you open up and have large numbers of people, kids and adults, in buildings, inside all day, can you do that safely? And I think most experts would say, not really, not if you’re in a hotspot. So, in places where things are really bad, I think it’s going to be really hard to open schools and keep them open.”