California has issued a “stay at home” order to residents as it tries to stem the march of the coronavirus across the most populous US state.
Governor Gavin Newsom told Californians they should only leave their homes when necessary during the pandemic.
He earlier estimated more than half of the 40 million people in his state would contract Covid-19 in just the next two months.
The virus has so far claimed 200 lives in the US and infected 13,678 people.
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Governor Newsom said: “This is a moment we need to make tough decisions. We need to recognise reality.”
His order will allow residents to leave their homes to buy groceries or medicine, or walk a dog or take exercise, but seeks to limit public interactions.
About half of the state’s population are already subject to similar stringent measures, including the city of San Francisco.
The Democratic governor said parts of the state were seeing infection rates double every four days.
He issued a dire prediction in a letter to President Donald Trump on Wednesday, appealing for urgent federal help.
“We project that roughly 56 percent of our population – 25.5 million people – will be infected with the virus over an eight week period,” Governor Newsom wrote.
So far, California has recorded fewer than 1,000 cases of the virus and 19 deaths, according to the Los Angeles Times.
Along with New York and Washington, California is among the US states worst hit by the coronavirus pandemic.
On Thursday alone, New York City’s recorded caseload of Covid-19 more than doubled to 3,954 – greater than the confirmed number of coronavirus patients in the whole of the UK.
Mayor Bill de Blasio told CNN the most populous city in the US would run out of medical supplies within three weeks if the “explosion” of infections continued at such a rate.
He implored the federal government to help New York obtain 15,000 ventilators, three million respirator masks, 50 million surgical masks and 45 million gowns, gloves and coveralls.