ST. PETERSBURG, Florida (AP) — Tensions mounted over how the United States is grappling with a resurgent coronavirus outbreak Monday, as global health officials warned that the pandemic will only intensify worldwide unless officials adopt comprehensive strategies to combat it.

The virus’ spread is worsening in many countries and “there will be no return to the old normal for the foreseeable future,” the director of the World Health Organization, Tedros Adhanom Ghebreyesus, said.

Tedros called for countries to come up with comprehensive strategies, and noted that roughly half of all new cases are in the Americas. His remarks came a day after Florida shattered the record among U.S. states for the largest single-day increase in new confirmed cases, with more than 15,000.

“If the basics aren’t followed, there is only one way this pandemic is going to go,” Tedros said. “It’s going to get worse and worse and worse.”

Meanwhile, two WHO experts were in China for a mission to trace the origin of the pandemic. The virus was first detected in central China’s city of Wuhan late last year. Beijing had been reluctant to allow a probe but relented after scores of countries called on the WHO to conduct a thorough investigation.

The probe comes as cases continue to rise in many U.S. states, especially in the South and West.

“I really do think we could control this, and it’s the human element that is so critical. It should be an effort of our country. We should be pulling together when we’re in a crisis, and we’re definitely not doing it,” said University of Florida epidemiologist Cindy Prins.

The U.S. totals are still well below the numbers reached in April, according to a recent Associated Press analysis of data from Johns Hopkins University.

But with President Donald Trump pressuring school districts to reopen this fall, and with the academic year in some southern states just weeks away, the debate over how to respond to the resurgence is growing more heated.

“I do think that there are going to be many challenges to opening schools safely and just kind of asserting that just because they want to open safely doesn’t make it so,” Dr. Tom Inglesby, director for the Center of Health Security at Johns Hopkins University, told a Fox News interviewer on Sunday.

Adm. Brett Giroir, a member of the White House coronavirus task force, called mask-wearing in public, which has been met with resistance in some U.S. states, “absolutely essential.”

Giroir, the assistant secretary at the Health and Human Services Department, told ABC’s “This Week” on Sunday that “if we don’t have that, we will not get control of the virus.”

Trump wore a mask in public for the first time Saturday, something Democratic House Speaker Nancy Pelosi said Sunday showed he has “crossed a bridge.”

In Florida, where parts of Walt Disney World reopened Saturday, 15,299 people tested positive, for a total of 269,811 cases, and 45 deaths were recorded, according to state Department of Health statistics reported Sunday.

California had the previous record of daily positive cases — 11,694, set on Wednesday.

The numbers come at the end of a record-breaking week as Florida reported 514 fatalities — an average of 73 per day. Three weeks ago, the state was averaging 30 deaths per day.

Regarding the WHO experts in China, the country’s Foreign Ministry spokesperson, Hua Chunying, said they would work with Chinese scientists and medical experts on “scientific cooperation on the new coronavirus tracing issue.”

China has argued that the virus might have originated outside of China and has angrily denied allegations that it covered up the scale of the outbreak as infections first began to spread.

Trump has harshly criticized WHO over its response to the coronavirus pandemic and accused it of bowing to Chinese influence. The Trump administration formally notified the U.N. last week of its withdrawal from WHO, although the pullout won’t take effect until July 6, 2021.

“We have a basic consensus with the WHO that virus tracing is a scientific issue, and that requires international scientific research and cooperation of scientists across the world,” Hua, the Chinese foreign ministry spokesperson, said. “WHO also believes that the virus tracing is an issue in progress, which may involve multiple countries and regions, and WHO will also conduct similar inspections in other countries and regions as needed.”

The WHO confirmed the visit by an epidemiologist and an animal diseases specialist but has not given out information on their agendas while in China. The virus causing the deadly illness COVID-19 is believed to have originated in bats and then jumped to humans via an intermediary species, possibly the anteater-like pangolin that is prized in China for its scales used in Chinese medicine as well as its meat.

In Japan, more than 30 Marines tested positive at the Futenma U.S. air station on Okinawa, where infections among American service members have rapidly risen to more than 90 since last week. Okinawa is home to more than half of about 50,000 American troops based in Japan.

Confirmed cases also have been found at three other Okinawa bases: 22 at Camp Hansen, one at Camp Kinser and another one at Camp McTureous. Officials said the movements of people at Futenma and Camp Hansen have since been restricted and large-scale virus testing is being conducted.

In other parts of the world, the number of infections has been rising dramatically in India, South Africa and Brazil, whose virus-denying president has tested positive.

India, which has the most confirmed virus cases after the United States and Brazil, on Monday reported a record daily surge of 28,701 new cases reported in the past 24 hours. Authorities in several cities are reinstating strict lockdowns after attempting to loosen things up to revive an ailing economy.

In South Africa, which accounts for over 40% of all the reported coronavirus cases in Africa, President Cyril Ramaphosa reimposed a ban on alcohol sales and reinstated a nighttime curfew to reduce the number of people needing emergency treatment so hospitals have more beds to treat COVID-19 patients.

“We are taking these measures fully aware that they impose unwelcome restrictions on people’s lives. They are, however, necessary to see us through the peak of the disease,” Ramaphosa said in a letter to the nation Monday. “There is no way that we can avoid the coronavirus storm. But we can limit the damage that it can cause to our lives.”