Los Angeles is offering free coronavirus tests to all residents, regardless of whether they are displaying any symptoms.
Mayor Eric Garcetti made the announcement just hours after Los Angeles County reported its largest daily increase in new Covid-19 cases.
Until now, only essential workers and those displaying symptoms could receive tests due to a scarcity of kits.
Meanwhile, California ordered all beaches in Orange County to close.
California is the most populous state in the US, and while some of its beaches have been closed for weeks, others have remained open with social distancing rules in place.
Over the weekend, photos of crowded beaches in the county, which is south of Los Angeles, led state governor Gavin Newsom to warn that the behaviour of some sun-seekers threatened to undo weeks of work to restrict the spread of Covid-19.
What's going on in Los Angeles?
Los Angeles County currently accounts for almost half of California's confirmed coronavirus cases. The state has so far reported over 48,000 cases and more than 1,900 deaths.
On Thursday, Mr Garcetti urged all of the city's residents to get swabbed after earlier tweeting that "LA is now the first major city in America to offer free Covid-19 testing".
Free COVID-19 testing is available to any L.A. County resident. https://t.co/13jZaOOegy— MayorOfLA (@MayorOfLA) April 30, 2020
Meanwhile, US media had expected Governor Newsom to sign an executive order to close all beaches and parks in the state after a memo circulated to the state's police chiefs indicated as much.
However, he restricted his order on Thursday to beaches in Orange County, saying "we are going to do a hard close in that part of the state".
The beaches would be closed until further notice, although he added that he hoped he would not have to maintain the order for too long.
California was among the first US states to bring in blanket restrictions, issuing a "stay at home" order to residents last month in an effort to stem the march of the coronavirus.
Mr Newsom recently said that he was still weeks away from lifting some restrictions.
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A grim milestone
By Sophie Long, BBC News, Los Angeles
Los Angeles Mayor Eric Garcetti's announcement of free testing for all came hours after a grim milestone - LA County saw it's largest increase in new Coronavirus cases reported in a single day since the pandemic began, though the rate of hospitalisations and percentage of people testing positive have remained stable.
Eric Garcetti urged all Angelenos to get swabbed. "You can't put a price on the peace of mind of knowing you can't infect someone around you" he said. California's leaders have long characterised expanding Covid-19 testing as one of a number of critical milestones that need to be met before stay at home orders can be modified.
While Los Angeles County, which is home to nearly 10 million people, continues to be the coronavirus hotbed of California, accounting for nearly half of the States' nearly 50,000 confirmed cases, that milestone could now be in sight.
In other US developments:
- Federal social distancing measures expire on Thursday. US President Donald Trump has said he will not renew them because governors can make decisions for individual states
- New York governor Andrew Cuomo said the state would start a "massive" contact tracing effort, hiring between 6,400 and 17,000 tracers
- Subways in the New York City area will shutdown for cleaning every night between 01:00 and 05:00 - one of the few times the 24-hour service has been halted. Essential workers who need to travel during those hours will be given free Uber and Lyft rides
- In the past week, 3.8 million more people filed for unemployment benefits in the US, meaning at least 30 million Americans have lost their jobs since mid-March
- The state of Georgia is temporarily allowing 16-year-olds to get drivers' licences without a road test during the pandemic
- Mr Trump stepped up his criticism of China over the outbreak, saying the country "will do anything they can" to make him lose in his re-election bid