Up to 30 million Californians are making last minute preparations before a strict three-week stay-at-home order begins in the lead-up to Christmas.

To stop another COVID-19 surge amid a worrying lack of intensive care beds in hospitals, the stay-at-home orders were to take effect on Sunday night (local time) in southern California, much of the San Francisco Bay area and other areas.

The rules prohibit residents from gathering with those outside their household. Bars, hair salons and barber shops must close, while restaurants can offer only takeaway or delivery.

The ABC reported the drastic restrictions were triggered by an “automatic cut-in” when the number of available ICU beds fall below 15 per cent.

“These regions have to kick up to this higher level of social restriction. That’s what’s happened here. That’s a worrying statistic to know such a large part of California is now at critically low levels of intensive care bed capacity,” the ABC’s Greg Jennett reported from the US on Monday.

Cars line up at LA’s Dodger Stadium for COVID-19 testing. Photo: Getty

On Sunday alone, California had 30,075 new COVID cases, far more than its previous record of 21,986 on December 4, as well as another record for hospitalised patients.

New Jersey, North Carolina, Virginia and West Virginia also announced record one-day rises in new infections.

Top US health officials are warning Americans that with a COVID-19 vaccine perhaps just days away, and with most of California heading in lockdown, this is no time to let their guard down.

Dr Deborah Birx, the White House coronavirus response co-ordinator, told NBC’s Meet The Press: “The vaccine’s critical but it’s not going to save us from this current surge. Only we can save us from this current surge.”

Tweet from @MeetThePress

A Food and Drug Administration advisory panel is scheduled to take up a request on Thursday to authorise emergency use of Pfizer’s vaccine.

Vaccinations could begin just days later, though initial supplies will be rationed and shots are not expected to become widely available until the northern hemisphere spring.

With the US facing what could be a catastrophic winter, top government officials warned Americans anew to wear masks, practice social distancing and follow other basic measures – precautions President Donald Trump and members of the administration have often disdained.

“I hear community members parroting back those situations – parroting back that masks don’t work, parroting back that we should work towards herd immunity, parroting back that gatherings don’t result in super-spreading events,” Dr Birx said on Sunday.

“I think our job is to constantly say those are myths, they are wrong and you can see the evidence base.”

The virus has been blamed for more than 280,000 deaths and more than 14.6 million confirmed infections in the US.

New daily cases have rocketed to a record high of more than 190,000 on average.

Deaths per day have surged to an average of more than 2160, a level last seen in April. On Sunday, the number of Americans in hospital with the coronavirus topped 100,000.

-with agencies