California governor has issued a “stay at home” order to residents as the state tries to stem the march of the coronavirus across the most populous US state.

Governor Gavin Newsom told residents 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.

Speaking from the state’s emergency operations centre in Sacramento – a place that is normally used to coordinate the response to wildfires or earthquakes – Governor Newsom called on people here to only leave their homes if it was absolutely necessary, to get food, collect medicines, or care for a friend or relative.

Citing a model that state planners here have been using, the governor predicted that more than half of California’s population will contract the virus over the course of the next eight weeks – a staggering total of around 25 million people.

Governor Newsom said that cases of the virus were doubling every four hours in some areas, and – based on projections – nearly 20,000 more hospital beds would be needed to deal with the effects of the outbreak than the state could currently provide.

The virus has claimed 205 lives in the US and infected more than 14,000.

Globally nearly 250,000 patients have tested positive for the respiratory illness and more than 10,000 have died.

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Governor Newsom said on March 19: “This is a moment we need to make tough decisions. We need to recognize reality.”

California is among the first states to bring in blanket restrictions. Earlier this week Nevada said non-essential businesses should close for 30 days.

The governor’s 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.

It will force businesses deemed non-essential to close, while allowing others including grocery stores, pharmacies, banks and petrol stations to stay open.

About half of California’s population is already subject to similar stringent measures, including the city of San Francisco.

Speaking at a press conference in Sacramento, Governor Newsom said the virus “will impact about 56% of us – you do the math in the state of California, that’s a particularly large number”.

The governor did not clarify how his officials had calculated that figure, which would amount to nearly 22.5 million infected people.

However, his spokesman acknowledged the estimate did not take into account the mitigation measures being implemented state-wide.

Governor Newsom is asking Congress for a billion dollars in federal funding to support California’s response to the crisis, and calling for a navy hospital ship to be deployed to the Port of Los Angeles to help deal with the anticipated surge in patients.