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.

The new, more contagious strain of the novel coronavirus, which is sweeping rapidly across London and other parts of southeast England, has been detected in California's San Bernardino County, officials said.

The latest variant of the virus that causes COVID-19 was found in two members of the same household in the Big Bear area who were tested on Dec. 20, according to a press release from the San Bernardino County Department of Public Health. One of them had contact with a traveler who returned from the United Kingdom on Dec. 11 and began showing symptoms three days later.

Four other cases of the fast-moving strain, known as B117, have been detected in San Diego County.

"Based on the information currently available, we know that the B117 variant strain seems to spread more easily and quickly," Dr. Michael Sequira, San Bernardino County public's health officer, said in a statement Friday. "Therefore, following all safe practices is more important than ever."

Experts say there's currently no evidence that the variant is deadlier or causes more severe illness, or that existing vaccines are less effective against it.

The new strain was announced in England in late December and then confirmed in the United States for the first time on Tuesday, after a case was detected in Colorado.

More than 4 million people in the United States have received their first dose of a COVID-19 vaccine, according to the Centers for Disease Control and Prevention.

As of 9 a.m. ET on Saturday, 13,071,925 vaccine doses had been distributed nationwide and 4,225,756 doses had been administered, according to the CDC COVID Data Tracker.

The doses include both the Pfizer/BioNTech and Moderna vaccines.

Public Health England does not recommend mixing COVID-19 vaccines from different suppliers, according to the agency's head of immunizations, Dr. Mary Ramsay.

"We do not recommend mixing the COVID-19 vaccines -- if your first dose is the Pfizer vaccine you should not be given the AstraZeneca vaccine for your second dose and vice versa," Ramsay said in a statement Saturday. "There may be extremely rare occasions where the same vaccine is not available, or where it is not known what vaccine the patient received. Every effort should be made to give them the same vaccine, but where this is not possible it is better to give a second dose of another vaccine than not at all."

The clarification comes amid questions over the British government's updated guidance on COVID-19 vaccines, which now says that if individuals who received the first shot go to an immunization site where that same vaccine is not available for a second shot, or if the first vaccine received is unknown, "it is reasonable to offer one dose of the locally available product to complete the schedule."

"This option is preferred if the individual is likely to be at immediate high risk or is considered unlikely to attend again," the guidance adds.

The guidance, which was updated Thursday, also notes that "there is no evidence on the interchangeability of the COVID-19 vaccines although studies are underway," and thus "every effort should be made to determine which vaccine the individual received and to complete with the same vaccine."

Next week, the United Kingdom is set to begin distribution of a COVID-19 vaccine developed by England's University of Oxford and manufactured by British-Swedish pharmaceutical giant AstraZeneca, after the drug was approved Wednesday for emergency supply. Another COVID-19 vaccine developed by U.S. pharmaceutical giant Pfizer and its German partner BioNTech was approved in the U.K. on Dec. 2 and rollout began a week later.

ABC News' Zoe Magee contributed to this report.