SACRAMENTO, CALIF. -- California on Thursday started requiring people throughout the state to wear masks in most indoor settings and outdoors when distancing isn't possible as the coronavirus continues to spread.

"Science shows that face coverings and masks work," Gov. Gavin Newsom said in a statement about the new order. "They are critical to keeping those who are around you safe, keeping businesses open and restarting our economy."

States including Michigan, New York, Maine, Delaware and Maryland already have statewide mask orders in place.

The order came as California broadly reopens its economy. In most counties, people can now shop, dine in at restaurants, get their hair done and go to church, among other things. As restrictions relax, coronavirus cases are increasing, something the state says was expected as more people get tested. More than 3,400 infected people were hospitalized as of Wednesday, the most since April.

The order requires people to wear masks when inside or in line for any indoor public spaces, in healthcare settings like hospitals and pharmacies, while waiting for or riding public transportation and in outdoor spaces where it's not possible to stay six feet (1.8 metres) apart from others.

Until now, the Democratic governor had allowed local governments decide whether to mandate masks, an issue that has become politically fraught as some Americans resist orders to wear them. Newsom said he issued the order because too many people are going out in public without face coverings as businesses, restaurants and other sectors of the economy reopen.

The public health officer in Southern California's Orange County resigned last week after she faced threats over her order that people wear masks, and the county sheriff said he wouldn't enforce it. Los Angeles County requires people to wear masks when outside their homes, as do San Francisco and Santa Clara counties.

Republican Assemblyman James Gallagher said he preferred letting locals decide and criticized Newsom for routinely changing his mind on who sets virus-related rules.

"The governor can't seem to make up his mind if counties can govern themselves during this pandemic. Perhaps if his guidance was more clear, Californians would be better prepared to meet this moment," he said in a statement.

Dr. Clayton Chau, Orange County's interim health officer, said the county is still reviewing the state's order, which would supersede his own. Chau last week changed Orange County's rules to recommend instead of require masks, and said he hasn't seen any data since that would make him question that decision.

Kate Folmar, a spokeswoman for the California Health and Human Services agency, said violating the order could bring a misdemeanour charge, a fine, or other penalties, or that California's Division of Occupational Safety and Health could take action against businesses.

But Mark Ghaly, the agency's secretary, said the department doesn't want to focus on enforcement and expects most Californians will comply.

"We believe that enough Californians are going to see this recommendation and carry it out, and it's going to allow us to make a substantial dent in transmission versus if we didn't do it collectively," he said.

Orange County Sheriff Don Barnes said it's an issue of individual responsibility, not law enforcement.

"County residents will continue to use common-sense approaches for the benefit of their own health, as well as the collective health of other county residents," he said.

Katrina Foley, mayor of the Orange County city of Costa Mesa, said the state's decision will take pressure off businesses by making it clear masks are required. Her city has required facial coverings even when the county hasn't.

"Nobody wants to have to arrest people for not wearing a facial covering. We just want people to care about others, so people don't die," she said.

The order also applies to workplaces where people interact with the public, prepare or package food and share common spaces like hallways and elevators. Office workers must wear masks if they can't physically distance.

It includes several exceptions, including for outdoor recreation and exercise such as walking, hiking, running or bicycling. But if people doing such activities can't stay six feet (1.8 metres) apart from others, the state says they should wear masks. Also outside, Ghaly said people should consider wearing masks if they are at a crowded intersection or in another space where they are close to others.

Brianna Sims, a 21-year-old grocery store worker in Sacramento, said she agreed with the order and that it's been a mixed bag among customers when it comes to people wearing masks.

Rey Kuvelis, 67, wore a mask as he walked home from a beer run in Sacramento on Thursday. He wears his mask whenever he leaves the house, but said he sees a lot of people without them.

"I would be very upset with myself if I cause like 10 people to get it because of my negligence," he said.

Other exceptions include: Children 2 and younger; people with medical conditions that prevent them from wearing masks; people who are deaf or with hearing loss and those who communicate with them; and people receiving treatments on their noses and mouths. There's also an exception if wearing a face covering would violate workplace safety guidelines.

People eating out at restaurants wouldn't have to wear masks while they are eating and drinking as long as they are six feet away f;om others.

For most people, the coronavirus causes mild or moderate symptoms, such as fever and cough. For some, especially older adults and people with existing health problems, it can cause more severe illness, including pneumonia, and death.

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Taxin reported from Orange County, California.