California Gov. Gavin Newsom urged residents to heed health warnings during the holiday season as the state's hospital system is pushed to the limit with COVID-19 patients.

He warned there could be multiple surges in cases "unless we are cautious and mindful about our travel plans this holiday season and about our proximity to people outside our households."

The number of the Intensive Care Unit patients is now 3,827, which was nearly double the 2,006 patients on Dec. 1, according to Newsom.

"On Monday, we were at 2.5% ICU availability and now as a state today, we are down to 1.1% ICU bed availability," he said.

"We had 8,517 people that were in our hospitals that tested positive for COVID-19 on Dec. 1st. Now 18,828 people are testing positive in just a three-week period," Newsom added.

-ABC News' Cammeron Parish contributed to this report

The new COVID-19 variant in the United Kingdom has likely infected tens of thousands of people, Jeffrey Barrett, director of the COVID-19 Genomics Initiative at the U.K. Wellcome Sanger Institute, said at a virtual Q&A hosted by the World Health Organization.

While there are just over 3,000 people who have the full genome sequence confirmed for the variant, only a small fraction of cases are sequenced, he said.

There’s no evidence the new variant is more deadly and it’s highly likely the vaccine will still work, officials said.

ABC News’ Sony Salzman contributed to this report.

Thursday, Dec. 24, Dr. Anthony Fauci’s 80th birthday, will be "Dr. Anthony S. Fauci" day in Washington, D.C., Mayor Muriel Bowser announced Wednesday.

"We are incredibly proud to count Dr. Fauci among the many DC residents who are sacrificing so much to keep our communities healthy and safe,” Bowser tweeted.

Hard-hit California reported 39,069 daily cases on Wednesday -- a 2% increase from Tuesday.

California’s daily cases are more than the daily cases in the United Kingdom, Russia, India, Italy and France, according to Johns Hopkins University data.

California is recording more than twice as many daily cases than the next hardest-hit states. Tennessee recorded 16,036 cases Tuesday and Texas had 16,607 cases, according to Johns Hopkins.

ABC News’ Bonnie Mclean contributed to this report.

An increasing number of children are being infected with multisystem inflammatory syndrome in children (MIS-C), according to a statement Saturday relased by Los Angeles County Board of Supervisors Chair Hilda L. Solis, supervisor to the First District.

"It is heartbreaking that every day, more than 14,000 Los Angeles County residents are testing positive for COVID-19. It is even more painful to see an increasing number of children being infected by MISC-C. There is a misconception that COVID-19 only impacts those who are older or those with underlying health conditions. At this point in the crisis, we can say for certain that COVID-19 causes severe consequences in people of all ages, including children, and even without underlying health conditions. In Los Angeles County, the Latinx community is bearing the brunt of COVID-19 and MISC-C cases," the statement read.

There have been 51 total cases of MIS-C in children, including one child death. All 51 children with MIS-C were hospitalized and nearly 50% of the children were treated in the intensive care unit. Of the children with MIS-C, 31% were under the age of 5 years old, 38% were between the ages of 5 and 11 years old, and 31% were between the ages of 12 and 20 years old. Latinx children account for nearly 73% of the reported cases, according to the statement.

Experts say the inflammatory syndrome resembles toxic shock syndrome and Kawasaki disease, itself a rare inflammatory disease typically affecting children under the age of 5, and has the potential to be deadly.

-ABC News' Matthew Fuhrman, Olivia Rubin and Soo Rin Kim