U.K. health authorities on Sunday reported 54,990 newly confirmed cases of COVID-19 and 454 additional deaths from the disease, bringing the respective totals to 2,654,779 cases and 75,024 fatalities.

"What we're doing clearly is grappling with a new variant of the virus which is surging particularly in London and the southeast," British Prime Minister Boris Johnson said on the BBC's Andrew Marr Show on Sunday.

Johnson said he felt it was important to stress that the threat to kids, young people and (school) staff "is really very very very small indeed" and that parents should send their children to primary school on Monday as long as they are open. But he warned they may need to impose tougher measures in many parts of the country.

"I'm fully fully reconciled to that," he said.

On Saturday, the United Kingdom's National Education Union (NEU) said in a statement that they have made the "difficult decision" to advise members in primary schools that it is unsafe for them to be in school due to "crowded buildings with no social distancing, no PPE and inadequate ventilation," and move to remote learning.

"If Government does not act to follow the science, we must," the NEU said.

-ABC News' Christine Theodorou

The Transportation Security Administration screened 1,192,881 people at airport security checkpoints across the United States on Saturday, the agency reported.

Sunday is expected to be the biggest travel day since the start of the pandemic.

-ABC News' Sam Sweeney contributed to this report.

A staggering 299,087 new cases of COVID-19 were confirmed in the United States on Saturday, according to a real-time count kept by Johns Hopkins University.

It's the highest tally of newly diagnosed COVID-19 infections that a country has recorded in a 24-hour reporting period since the start of the pandemic.

An additional 2,398 deaths from COVID-19 were also registered nationwide on Saturday, down from a peak of 3,750 on Dec. 30, according to Johns Hopkins data.

COVID-19 data may be skewed due to possible lags in reporting over the holidays followed by a potentially very large backlog.

A total of 20,430,088 people in the U.S. have been diagnosed with COVID-19 since the pandemic began, and at least 350,214 of them have died, according to Johns Hopkins data. The cases include people from all 50 U.S. states, Washington, D.C., and other U.S. territories as well as repatriated citizens.

Much of the country was under lockdown by the end of March as the first wave of pandemic hit. By May 20, all U.S. states had begun lifting stay-at-home orders and other restrictions put in place to curb the spread of the novel coronavirus. The day-to-day increase in the country's cases then hovered around 20,000 for a couple of weeks before shooting back up over the summer.

The numbers lingered around 40,000 to 50,000 from mid-August through early October before surging again to record levels, crossing 100,000 for the first time on Nov. 4 and reaching 200,000 for the first time on Nov. 27.

More than 1,600 fines have been issued and several people have been arrested following a days-long, illegal New Year's Eve party in northwestern France, authorities said.

Despite a national nighttime curfew and other strict measures in place due to the coronavirus pandemic, some 2,500 people attended the rave on Thursday night in an empty warehouse located in the small village of Lieuron in France's scenic Brittany region, a popular vacation spot. Some partygoers clashed with local police when they tried to shut down the illegal rave, injuring several officers and damaging their vehicles, according to authorities.

The violence prompted officers to await reinforcements from the National Gendarmerie before moving in and putting an end to the party Saturday morning, as revellers finally began to disperse, authorities said.

At least five people, including the two organizers of the rave, have since been taken into custody. Trucks, various sound equipment, narcotics and large sums of cash have also been seized from the site, according to authorities.