Michigan and Washington are the latest US states to bring in strict measures to try and curb the spread of Covid-19.
High schools and colleges are to halt on-site teaching and 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.
Covid cases have now topped 11 million in the US, with hospital admissions at record levels.
On average, more than 1,000 people a day are dying with the virus, and the overall death toll is close to 250,000.
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.
But aides to President-elect Joe Biden say the White House's refusal to facilitate a presidential transition means his team is being excluded from planning around a vaccination campaign that will be a priority for Mr Biden when he takes office in January.
"Our experts need to talk to those people as soon as possible so nothing drops in this change of power we're going to have on January 20th," the president-elect's chief of staff Ron Klain was quoted as saying by the Associated Press news agency.
Mr Klain said the Biden team would nonetheless start talking to vaccine manufacturers, including Pfizer.
President Donald Trump has continued to claim he won the 3 November election, tweeting late on Sunday night: "I WON THE ELECTION!"
Twitter affixed a warning label to the tweet reading: "Official sources called this election differently."
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?
Both Michigan and Washington State 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."
What's the situation elsewhere in the US?
California on Friday became the second state, after Texas, to hit one million Covid cases, prompting local officials to hit pause on reopening efforts.
In other developments:
- 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; the city could also close schools on Monday
- 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.
- Tracking the global pandemic: Where has been hit hardest?
- Is the Covid vaccine safe for me? And other questions
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.
- EASY STEPS: How to keep safe
- HOPE AND LOSS: Your coronavirus stories
- VIDEO: The 20-second hand wash
- STRESS: How to look after your mental health