Schools and tourist attractions across the San Francisco Bay Area were closed Friday as smoke from California's deadliest ever fires more than 150 miles (240 kilometers) away produced air quality levels worse than polluted cities in South Asia and China.
All public schools were ordered shut, according to an official notice, while the picturesque coastal city's iconic cable cars were sent back to their stations as the Air Quality Index soared to 213, comparable to Dhaka, Bangladesh and worse than Kolkata.
"San Francisco's air quality has moved from red or 'unhealthy' to purple or 'very unhealthy' due to local wildfires and weather patterns," the SFMTA transport authority said on its website.
"The Department of Public Health highly recommends that everyone stay indoors and avoid exposure to the outside air."
Mayor London Breed announced that all Muni buses would be free for the day in order to ensure people have access to enclosed transportation.
Photos posted on social media showed the famous Golden Gate bridge shrouded in thick smog.
Wildfires that continue to ravage northern California have left at least 63 people dead, with hundreds still missing.
President Donald Trump is set to visit the western state on Saturday to meet with victims of the wildfires, believed to be the deadliest and most destructive in the state's history.
