Philadelphia will ban indoor gatherings altogether and the New Jersey will strictly limit their size as US officials struggle to slow a COVID-19 surge that could overwhelm hospitals and kill thousands.
Philadelphia, the nation's sixth-largest city, is strongly urging residents to shelter at home and "prohibiting indoor gatherings of any size in any location, public or private," health commissioner Thomas Farley said on Monday.
"We need to keep this virus from jumping from one household to another," Farley said.
If "exponential" growth of cases continues, hospitals will soon become overwhelmed and more than 1000 people could die in Philadelphia over the next six weeks before the end of the year, he said.
In neighboring New Jersey, Governor Phil Murphy on Monday said a maximum 10 people will be allowed to gather indoors, down from 25.
On November 23, the limit for outdoor gatherings will drop from 500 to 150.
"It's gotten worse and it's gonna get worse," the Northeastern state's Democratic governor told MSNBC.
By Monday, more than 70,000 people were hospitalised with coronavirus infections in the United States, an all-time high.
Total US infections crossed the 11 million mark, just over a week after hitting 10 million, the fastest time it took the country to report an additional 1 million cases since the pandemic began.
States across the nation have re-imposed restrictions to stem the tide, straining healthcare systems.
In California, Governor Gavin Newsom tightened restrictions, ordering many non-essential businesses to close in 41 counties where the vast majority of the state's 40 million residents live.
Newsom reactivated plans to add additional capacity to the hospital system, amid a doubling of COVID-19 cases in the past 10 days.
Dr Alexander Garza, head of the St. Louis Metropolitan Pandemic Task Force, said hospitals in Missouri could run out of capacity in two weeks as cases there continue to rise.
Forty US states have reported record increases in COVID-19 cases in November, while 20 have seen a record rise in deaths and 26 reported record hospitalisations.
The latest seven-day average shows the US is reporting more than 148,000 daily cases and 1120 daily deaths. Hospitalisations hit an all-time high on Sunday.
In Ohio, where total cases have increased about 17 per cent and total hospitalisations at least 25 per cent in the past seven days, health officials issued a revised order to limit mass gatherings from Tuesday.
In what she called the re-enactment of the "most heightened level of statewide" coronavirus restrictions, New Mexico Governor Michelle Lujan Grisham instructed residents to stay home for two weeks beginning on Monday, among other curbs.
"We face a life-or-death situation and we cannot fail to act," Grisham wrote on Twitter.
Michigan and Washington state on Sunday imposed sweeping new restrictions on gatherings, including halting indoor restaurant service.
The slew of grim records and news was partly offset by Monday's announcement by drugmaker Moderna its experimental vaccine is 94.5 per cent effective, based on interim data from a late-stage trial.
Together with Pfizer Inc's vaccine, also more than 90 per cent effective, and pending more review, the US could have two vaccines authorised for emergency use in December with as many as 60 million doses available this year.