California has ordered some bars to close as the state and a dozen others in the US face the worst surge in coronavirus cases since the start of the pandemic.
Governor Gavin Newsom's order is the first major rollback of efforts to reopen California's economy.
Bars in seven counties, including Los Angeles, must close and those in eight more counties are strongly recommended to shut their doors.
In Arizona, another state with a major outbreak, temperatures were expected to rise above 38C on Sunday along the Salt River east of Phoenix.
On Saturday, dozens of people climbed into inflatable inner tubes with coolers and took to the water to escape the heat. Very few wore masks.
Texas shuttered tubing and rafting business on Friday and some beaches in Florida are closing again before next weekend's Fourth of July holiday to try to curb the rising outbreak.
The surge in COVID-19 cases has been most pronounced in a handful of southern and western states that reopened earlier and more aggressively, despite warnings by health officials.
For a third consecutive day on Saturday, the number of confirmed US cases rose by more than 40,000, one of the largest surges in the world.
In Arizona, cases have risen by 267 per cent so far in June and jumped by a record 3857 cases on Sunday, the eighth record-breaking increase this month.
Even in states where cases have been declining for weeks, outbreaks are happening.
One bar in East Lansing, Michigan, has been linked to more than 85 cases, according to the Ingham County Health Department.
Just a day after he said the country was in "a much better place", Vice-President Mike Pence cancelled events to campaign for President Donald Trump's re-election in Florida and Arizona due to the outbreak.
Pence told CBS he was confident there were enough healthcare supplies and capacity to deal with the spike in cases.
He also defended Trump's refusal to directly ask Americans to wear masks or to wear one in public himself, even as Texas Governor Greg Abbott and others say the widespread use of masks will be critical to be able to reopen the economy.
"We believe people should wear masks wherever social distancing is not possible, wherever it's indicated by either state or local authorities," Pence told CBS.
On Sunday, Pence travelled to Texas and attended a service at the First Baptist Church of Dallas where a 100-member choir sang without masks. Pence did wear a face covering while sitting in the audience, according to a video.
US House Speaker Nancy Pelosi has criticised the administration's response to the pandemic that has killed more than 125,000 Americans, telling ABC News on Sunday that mandating the use of masks across the country was long overdue.
Global coronavirus cases exceeded 10 million on Sunday, marking a major milestone in the spread of the respiratory disease that has so far killed half a million people in seven months.
Australian Associated Press