A record number of more than 1,900 children were hospitalized with COVID-19 in the United States on Saturday, as hospitals across the South were stretched to capacity fighting outbreaks caused by the highly transmissible Delta variant.

The Delta variant, which is rapidly spreading among mostly the unvaccinated portion of the U.S. population, has caused hospitalizations to spike in recent weeks, driving up the number of pediatric hospitalizations to 1,902 on Saturday, according to data from the U.S. Department of Health and Human Services.

Children currently make up about 2.4 percent of the nation's COVID-19 hospitalizations. Kids under 12 are not eligible to receive the vaccine, leaving them more vulnerable to infection from the new, highly transmissible variant.

"This is not last year's COVID. This one is worse, and our children are the ones that are going to be affected by it the most," Sally Goza, former president of the American Academy of Pediatrics, told CNN on Saturday.

The numbers of newly hospitalized COVID-19 patients aged 18-29, 30-39 and 40-49 also hit record highs this week, according to data from the U.S. Centers for Disease Control and Prevention (CDC).

The spike in new cases has ramped up tension between conservative state leaders and local districts over whether school children should be required to wear masks as they head back to the classroom this month.

School districts in Florida, Texas and Arizona have mandated that masks be worn in schools, defying orders from their Republican state governors that ban districts from imposing such rules. The administration of Florida Governor Ron DeSantis has threatened to withhold funding from districts that impose mask requirements, and Texas Governor Greg Abbott is appealing to the state Supreme Court to overturn Dallas County's mask mandate, the Dallas Morning News reported on Friday.

A fifth of the nation's COVID-19 hospitalizations are in Florida, where the number of hospitalized COVID-19 patients hit a record 16,100 on Saturday, according to a Reuters tally. More than 90 percent of the state's intensive care beds are filled, according to data from the Department of Health and Human Services.

The U.S. now has an average of about 129,000 new COVID-19 cases per day, a rate that has doubled in a little over two weeks, according to a Reuters tally. The number of hospitalized COVID-19 patients is at a six-month high, and an average of 600 people are dying each day of COVID-19, double the death rate seen in late July.

Read more: U.S. witnesses uptick of COVID-19 child cases