Michigan, Washington and California are the latest US states to bring in strict measures to try to curb the spread of Covid-19, as cases top 11 million.
High schools and colleges are to halt on-site teaching while restaurants are prohibited from offering indoor dining in Michigan from Wednesday.
Indoor restaurant dining is also banned in Washington State, and gyms, cinemas, theatres and museums will close.
And much of California will return to its most severe restriction level.
On average, more than 1,000 people a day are dying with the virus, and the overall death toll is close to 250,000. Hospital admissions have also reached record levels with nearly 150,000 new cases across the US on Monday.
The Trump administration struck an optimistic note on Friday, saying it hoped to distribute 20 million doses of an approved vaccine in December, and for each month after that - although vaccines have yet to get official approval.
President-elect Joe Biden said on Monday that "people may die" because of the White House's refusal to facilitate a presidential transition and co-ordinate with the Biden team for a vaccination campaign. The lack of cooperation is "totally irresponsible", he said.
On Monday, in a major new development, US drug company Moderna said its Covid-19 vaccine was nearly 95% effective according to early results.
A similar announcement earlier this month about another vaccine - from the companies Pfizer and BioNTech - sent stock markets soaring amid hopes that life could return to normal next year.
Mr Biden celebrated the developments, but cautioned that distributing a vaccine to Americans is "a huge, huge, undertaking".
Even without coordination between the president and the president-elect, aides to Mr Biden have said his team would nonetheless start talking to vaccine manufacturers.
President Donald Trump on Monday celebrated the news and appeared to claim credit for the vaccine progress, writing on Twitter that these "great developments...all took place on my watch".
Mr Trump has ruled out putting the nation into lockdown, but many states are introducing their own restrictions as fast rising cases threaten to overwhelm their healthcare systems.
How worried are the state governors?
Michigan, Washington State and California have seen Covid cases double in recent weeks.
Michigan's Governor Gretchen Whitmer said the state was "at the precipice" and could soon suffer 1,000 coronavirus-related deaths a week unless action is taken.
As well as suspending in-person teaching and indoor dining, Ms Whitmer also ordered the closure of public entertainment venues for a period of three weeks.
The curbs announced in Washington State come into effect on Monday evening and will last a month.
"Today, Sunday, November 15, 2020, is the most dangerous public health day in the last 100 years of our state's history," Governor Jay Inslee said.
"A pandemic is raging in our state. Left unchecked, it will assuredly result in grossly overburdened hospitals and morgues; and keep people from obtaining routine but necessary medical treatment for non-Covid conditions."
On Monday, California Governor Gavin Newsom said he was pulling the "emergency brake", bringing more than 94% of the population under the strictest coronavirus guidance. In these counties, indoor restaurant spaces, worship spaces and gyms will be closed. Mr Newsom said he is also considering a state curfew to help slow the spread.
He also apologised on Monday for his "bad mistake" in attending a lobbyist's birthday party that violated his own coronavirus-prevention rules.
It emerged on Friday that he and his wife attended the celebration on 6 November at a Michelin-starred restaurant in wine country near San Francisco.
"The spirit of what I'm preaching all the time was contradicted," Mr Newsom said. "I need to preach and practise, not just preach."
California on Friday became the second state, after Texas, to hit one million Covid cases, prompting local officials to hit pause on reopening efforts.
What's the situation elsewhere in the US?
In other developments:
- Oregon and New Mexico brought in tighter restrictions on Saturday.
- Republican governors in Iowa, Ohio, West Virginia, Utah and North Dakota issued mask mandates
- Ohio's governor threatened to shut bars and gyms if the outbreak worsens
- In Minnesota, bars and restaurants must shut by 22:00 local time
- Wisconsin and Nevada residents were asked to stay at home for two weeks to avoid a return to restrictions
- The Democratic governors of California, Oregon and Washington State issued a travel advisory, discouraging non-essential travel and requesting people to quarantine post-travel
- New York ordered bars and restaurants that serve alcohol to close by 22:00 local time; gatherings are limited to 10 people; public schools on Monday remained open, but possible closures still loom
- The city of Chicago has a stay-at-home advisory, and non-essential businesses must close by 23:00 local time; gatherings are limited to 10 people
- The city of Detroit moved all students to remote learning due to the virus spikes
- Indiana halted reopening and limited social gatherings and events
- Maryland ordered restaurants to reduce indoor capacity to 50%
Concerns as another holiday approaches
Outbreaks in the spring and summer followed US schools' spring breaks and the national Labor Day holiday weekend - and now experts are concerned that as Thanksgiving approaches on 26 November, the spikes will again worsen.
That is the situation playing out across the border in Canada, where people celebrated their Thanksgiving a month ago. The country's top doctors say that the holiday is partly why cities and provinces are now seeing record infections.
Data shows that the majority of the US has rising "community spread" of the virus - situations where people get the virus without any known contact with a sick person.
Indoor gatherings pose a large risk to spreading the virus, and as the holiday centres around eating together, wearing masks is not feasible.
One analysis from Georgia Institute of Technology researchers found the risk of having a Covid-positive individual at even a gathering of 10 people could be close to 100% in the worst-hit parts of the US.
Back in October, top infectious diseases expert Dr Anthony Fauci cautioned that the "sacred" American tradition of gathering together at Thanksgiving was "a risk".
"You may have to bite the bullet and sacrifice that social gathering, unless you're pretty certain that the people that you're dealing with are not infected," Dr Fauci told CBS News.