California and Texas have both recorded record surges in the number of coronavirus infections, as nationally cases rise by more than 40,000.
Statewide positive tests for Covid-19, rose by at least 7,418 in California on Monday to nearly 223,000, the biggest one-day increase since tracking began.
Los Angeles County reported an “alarming” rise that put it over 100,000 cases, a Reuters tally showed.
With a population of 10 million people, Los Angeles County has become a new epicentre in the pandemic as California Governor Gavin Newsom orders bars to close and residents to wear masks in most public places.
Barbara Ferrer, director of public health for Los Angeles County, said: “The alarming increases in cases, positivity rates and hospitalizations signals that we, as a community, need to take immediate action to slow the spread of Covid-19.
“Otherwise, we are quickly moving toward overwhelming our healthcare system and seeing even more devastating illness and death.”
Ahead of Independence Day weekend, Los Angeles County said its beaches will be closed and firework displays banned.
Mayor Eric Garcetti has put a "hard pause" on reopening dates for cinemas and theme parks.
Texas, Florida and Arizona are among a number of US states fighting a new rise in infections as lockdown restrictions change.
Twenty-two US states have reported record increases this month, including Alaska, Arkansas, Montana, New Mexico, North Carolina, Oregon and Utah.
Coronavirus infections in Texas increased by 6,545 on Monday to nearly 160,000, also setting a record for a one-day increase.
Texas and Florida both ordered the closure of recently reopened bars on Friday as both states report new cases.
Beaches in Florida's Broward County, Palm Beach County and Miami-Dade County will not open for Independence Day weekend.
Nationally, cases rose by more than 40,000, for the fourth
time in the past five days.
US Vice-President Mike Pence is due to visit Arizona on Wednesday to discuss the new wave of infections.
Public schools in the state will not reopen until at least August 17.
Governor Dough Ducey has also ordered bars, nightclubs, gyms, cinemas and water parks to close for at least 30 days.
He said: "Our expectation is that next week our numbers will be worse."