LOS ANGELES — California, the most populous US state, has ordered its residents to stay at home as it tries to prevent the spread of the coronavirus.

In the most dramatic preventive measure yet by a US state, Gavin Newsom issued a directive, asking residents not to leave their homes but when necessary during the pandemic.

"There is a recognition of our interdependence that requires of this moment that we direct a statewide order for people to stay at home," he said.

No end date was set for the measure because the pandemic is a "dynamic situation," said Newsom.

The governor estimated that more than half of the 40 million people in his state would contract Covid-19 in just the next two months.

The virus has infected more than 14,000 people and killed 205 in the US. Globally nearly 250,000 patients have tested positive for the respiratory illness and more than 10,000 have died.

"People I think recognize the need to do more, and to meet this moment, and people will self-regulate their behavior," the Democratic governor said.

Essential jobs and tasks such as grocery shopping would be exempt, he said.

"We want people to go to essential jobs — we want people to deal with their essentials in a thoughtful and judicious way."

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 the state's population is already subject to similar stringent measures, including the city of San Francisco.

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

But his spokesman acknowledged the estimate did not take into account the mitigation measures being implemented state-wide. — Agencies