White House officials have been circulating a proposal that would give U.S. border authorities the extraordinary ability to block U.S. citizens and permanent residents from entering the country from Mexico if they are suspected of being infected with the novel coronavirus, according to two administration officials and a person familiar with the plans.

It is unclear whether the Trump administration has the legal authority to block citizens and permanent residents from returning to their own country, but one official said the administration is weighing a public health emergency declaration that would let the White House keep out potentially infected Americans.

Medical experts have warned the administration that such restrictions would make little difference in controlling the pandemic, because widespread community transmission already is occurring in the United States. The country’s outbreak is the world’s worst, with more than 5 million confirmed cases and wide circulation in many parts of the country, especially in the South and Southwest.

Arizona reported a record number of hospitalizations on July 2 due to a spike of covid-19 cases. Health workers urged the public to wear masks and stay home. (The Washington Post)

There is sharp dissent within the administration about the plan to keep sick Americans from traveling back into the country. The administration’s discussions were first reported by the New York Times on Monday.

Though the disease is widely circulating in South Texas, Arizona and in other border areas, with active community transmission on both sides of the line, President Trump continues to talk about the Mexican border as a source of the disease, using that argument to promote the barrier he is building there as a protective shield against the virus.

The Trump administration already has cited the pandemic to impose a rapid-expulsion system at the border that immediately returns to Mexico most migrants taken into U.S. Border Patrol custody.

If implemented, the proposals to temporarily block the ability of U.S. citizens to return home would be the first time the administration attempts to apply such restrictions to the hundreds of thousands of U.S. citizens and permanent residents who cross the border legally each day. The administration has restricted nonessential travel, but those crossing for school, work, business or medical appointments are generally not restricted.

As the virus continues to run rampant in the United States, the American Academy of Pediatrics and the Children’s Hospital Association reported that more than 97,000 U.S. children tested positive for the virus during the last two weeks of July, accounting for more than a quarter of the total number of children diagnosed nationwide since March. It was the latest sign of how the deepening pandemic has reached every corner of the nation and every demographic.

The report, which cited data from 49 states as well as territories such as Puerto Rico and Guam, also found that more than 380,000 cases have been reported in children since the pandemic began.

The number represented about 9 percent of total cases in the United States at the end of July, the authors said. As the total U.S. tally of coronavirus cases has risen past 5 million confirmed infections, there have been nearly 160,000 deaths — far more than any other country. As of April 14, people younger than 19 made up just 2 percent of cases nationwide, according to the data.

“It will be a little hard to sort out the degree to which a lot more kids are getting infected and the degree to which our testing capacity has gone up,” Sean O’Leary, a member of the American Academy of Pediatrics and professor of pediatric infectious diseases at the University of Colorado, said Monday. “What we can say is that it’s not particularly surprising, given the large increase in cases we’ve seen nationally overall.”

The jump in pediatric cases comes as children are entering close quarters for the first time in months as some of the nation’s schools begin to open their doors.

Many school districts are going forward with remote-only operations until local case numbers drop. Some have opted for hybrid learning systems in which children attend school in person only periodically, to limit crowding. But even some of the schools with measures to reduce the number of students present have suffered outbreaks.

North Paulding High School, near Atlanta, made news last week when pictures appeared on social media showing students crowded in hallways and not wearing masks. On Sunday, the school sent a letter to parents announcing that the campus would be closed to in-person learning for at least two days after nine people tested positive for the virus.

Asked at a White House news conference Monday about the report on youngsters and coronavirus infections, Trump said children account for a “tiny fraction” of virus deaths and added that in general “they get better very quickly.”

“I think schools have to open,” the president said, adding, “I think it’s a very important thing for the economy to get the schools open.”

Seven out of 10 new pediatric cases were reported in Southern and Western states, according to Monday’s report. Arizona reported the most cases per capita among children, with more than 1,000 per 100,000 on July 30. Louisiana, South Carolina and Tennessee were the only other states with more than 800 cases per 100,000.

O’Leary noted that a slight increase in the percentage of children who tested positive and were hospitalized from May (0.8 percent) to July (1.4 percent) might suggest that more children are getting sick. Unlike testing, which doesn’t necessarily indicate the severity of illness and isn’t uniformly available, hospitalization data is less subject to local circumstances and more directly related to the number of people falling ill.

O’Leary also noted limitations with the data, because they lack more granular information about age, race and ethnicity, and severity of illness.

Pediatric coronavirus deaths remain rare, accounting for less than 1 percent of the national total, the report concluded. Children also still make up a relatively small percentage of those hospitalized with the virus nationwide, but a report from the Centers for Disease Control and Prevention on Friday found that Hispanic and Black children were substantially more likely to be hospitalized with the disease than their White peers.

Teachers in the United States have threatened strikes as the unusual academic year begins. Schools have reopened and watched cases surface quickly. Districts that spent the summer planning hybrid systems, in which children would attend school part time, have scrapped those models as cases surged. Universities have altered start dates and their rules for housing, all with scant notice. And many school districts have yet to make final decisions about the fall, even as the end of summer approaches.

The turmoil comes as families and businesses around the country juggle the inevitable demands and desires to return to normal with the reality of a virus that continues to spread wherever people gather in large numbers.

One month after reopening, for instance, Walt Disney World is modifying its hours of operation in a schedule taking effect Sept. 8, the day after Labor Day. Disney’s already limited hours will be reduced by one to two hours per day, depending on the park. The change comes days after Disney reported unexpectedly low park attendance and “adversely impacted” earnings because of restrictions aimed at preventing the virus’s spread.

Meanwhile, with the cancellation of the college football season under serious consideration, the president joined members of Congress and athletes opposed to the move on Monday.

“The student-athletes have been working too hard for their season to be canceled. #WeWantToPlay,” Trump tweeted Monday afternoon. He tweeted again 51 minutes later: “Play College Football!”

The ongoing struggles have not been limited to the United States, even as it remains the epicenter of the pandemic.

British Prime Minister Boris Johnson said Sunday that the government has a “moral duty” to ensure students return to classrooms in September, potentially setting up a conflict with members of the opposition Labour Party who have questioned whether adequate safety measures are in place.

Health Minister Helen Whately told Sky News: “Sadly, we have seen children from more disadvantaged backgrounds [are] more likely to fall behind during this time, so it is essential that we have children back at school this autumn.”

Andy Burnham, the mayor of greater Manchester, has expressed hesitation about that plan, telling “BBC Breakfast” on Monday that better contact tracing must be put in place first. The children’s commissioner for England and Britain’s National Education Union has also called for regular coronavirus testing in schools.

Coronavirus cases have risen in several European countries in recent weeks, prompting some governments to implement new public health guidelines to keep transmission under control.

In Paris, anyone older than 11 is required to wear a mask in many outdoor spaces. About 400 cases are being confirmed each day in the Paris area, with many of those cases diagnosed in people ages 20 to 30.

In Germany, where students are starting to return to school, new protocols were put in place at airports over the weekend, mandating tests for travelers arriving from countries deemed high risk for coronavirus infections.

In Spain, hospitalizations have quadrupled in the past month, the Spanish newspaper El Pais reported Monday. In Ireland, 174 new cases were confirmed on Saturday, marking the highest number of cases recorded there in about three months.

Rick Noack, Antonia Farzan, Shannon McMahon and Siobhán O’Grady contributed to this report.