The Bay Area’s already fetid, wildfire-choked air continued to register “very unhealthy” levels of particulate matter throughout the region Friday morning, following public health warnings and mass closures of schools, universities, businesses — even San Francisco’s fabled cable cars were pulled off the hills.

Firefighters have made progress containing the deadly Camp Fire in Butte County, but it’s become clear that the sickly haze has settled over the area for the foreseeable future.

Since Thursday, fire-ravaged Northern California has had the dirtiest air in the world, topping notoriously smoggy cities in India and China, according to air quality monitoring network Purple Air. The Butte County Air Quality Management District reported “hazardous” air quality in Chico, Oroville and Sacramento.

Data from the Bay Area Air Quality Management District showed local air quality levels in the “very unhealthy” range.

The National Weather Service predicted that smoke will continue to plague the region into next week. “The winds are light and offshore, so there’s nothing to move the smoke,” said Suzanne Sims, a meteorologist with the National Weather Service. “It’s there, and it’s not going anywhere.”

Fine particles from the wildfire smoke can settle in lungs and irritate respiratory systems. Children, older adults and people with heart or lung conditions are especially at risk when air quality diminishes. But the air became so bad in the last 24 hours that it was considered hazardous to all people, regardless of medical conditions.

Public health officials have urged residents to stay indoors and keep N95 masks on when outdoors. Some city governments and independent organizations are giving out face masks to those in need.

The city has created a map of filtered air shelters, including branches of the San Francisco Public Library and Westfield San Francisco Centre.

Workers scurried home along San Francisco’s sidewalks Thursday evening wheezing, coughing and gasping for clean air. Filtration masks were hard to come by, as were air purifiers. Downtown workers and residents in search of masks lined up at the Cole Hardware store on Fourth Street. At lunch time the line was 75 people deep and customers were limited to four masks, a number that was reduced to two as supply dwindled.

Michael Costa, a salesman at Cole Hardware, estimated that more than 3,000 masks had been sold by 5 p.m. A shipment of air purifiers that arrived Thursday morning was gone within a few minutes. A sign at the front of the store said, “We apologize that we are sold out of N95 masks.”

All public schools in San Francisco, Alameda, Contra Costa, Solano and Marin counties canceled Friday classes, citing poor air quality. Schools in Santa Clara County planned to remain open but were canceling outdoor activities or moving them indoors. In Napa County, the Napa Valley Unified School District and the St. Helena Unified School District were closing, as did schools in San Mateo County.

Colleges and universities throughout the region — including San Francisco State University, San Jose State University and UC Berkeley — also canceled classes Friday.

San Francisco officials shut down cable car service Thursday afternoon and declared that Muni would be free Friday to help people avoid bad air outside while moving about the city. Mayor London Breed urged residents to stay indoors until conditions improve.

A smattering of disappointed tourists showed up Thursday evening at the cable car turnaround at Powell and Market streets. Cleveland resident Cyrus Rai, in town for a week with his wife and three children, had planned on excursions to Fisherman’s Wharf, Alcatraz and the Golden Gate Bridge. Instead he started the day at the hardware store buying masks.

“We canceled all our plans,” he said. “We are going to go to the mall to do some shopping or something like that.”

Some Bay Area residents made the spontaneous decision to drive off in search of clearer air. Berkeley resident Micha Oliver, whose 5-year-old son, Sammy, suffers from asthma, spent much of the day researching the latest air quality data to figure out where to go. She has three air purifiers in her house, but even with all three cranked up, the air in her house was unhealthy. She considered San Luis Obispo and Santa Barbara before settling on Incline Village in Tahoe.

“We are loading up our car and getting out,” she said. “The air is getting worse and worse. I wouldn’t want a regular 5-year-old boy breathing this air, let alone one with severe asthma.”

Marin residents Priya and Alex Clemens also made a spontaneous decision to escape the smoke after both their sons were sent home from school with bloody noses. By 5 p.m., they were packing the car and motoring off to stay with grandparents in Yorba Linda (Orange County). “It was a snap decision,” said Alex Clemens, a lobbyist. “We are lucky we are in a position where we can go — that is not true for a lot of people.”

Parker Gibbs, a partner at the San Francisco music production company Light Rail Studios, said as poor as the air quality has been here, Bay Area folks should not lose sight of the bigger picture. “That smoke that is stinging our eyes, that is someone’s retirement home, that is someone’s hopes and dreams,” he said. “We may be dealing with an inconvenience, but those people lost everything.”

Gwendolyn Wu and J.K. Dineen are San Francisco Chronicle staff writers. Email: gwendolyn.wu@sfchronicle.com, jkdineen@sfchronicle.com Twitter: @gwendolynawu, @sfjkdineen