Health officials are urging the elderly and people with breathing problems to stay indoors due to the poor air quality caused by fallen ash and acrid smoke during the Southern California wildfires.

Satellite images showed thick smoke from more than a dozen wind-driven blazes blanketing a wide swath from Malibu to the Mexican border. State air regulators warned that the region's air quality has deteriorated since Sunday with concentrations of soot particles at unhealthy levels.

The South Coast Air Quality Management District has received dozens of calls from concerned parents wanting to know how to protect their children from the pollution.

"Our answer is to use common sense. If you can see smoke or falling ash, that means it's time to start curtailing your outdoor activity," said agency spokesman Sam Atwood.

The unhealthy air was expected to linger as long as the wildfires burn. It can take up to two days for the smoke to clear once the blazes are put out, experts say. The last time the air was this polluted was in 2003 when massive wildfires raged around the state.

Workers at the Del Mar Fairgrounds near San Diego put out a call Tuesday for more face masks for evacuees.

Kina Paegert, who has asthma, made sure to carry her inhaler and was told by paramedics to change her mask every four hours.

"You can hear it in my voice. I'm not usually this raspy," said Paegert, an information officer for the Del Mar Fairgrounds.

At the Henry Mayo Newhall Memorial Hospital in the Santa Clarita Valley north of Los Angeles where fires were burning, 22 people arrived at the emergency room complaining of respiratory problems, most likely from the smoke. At least two stayed overnight, hospital spokeswoman Bhavna Mistry said.

Sixteen patients, including four firefighters, were treated for burns at the University of California San Diego Medical Center. Of those, five also suffered from smoke inhalation.

Hospital spokeswoman Nancy Stringer said the medical center expected to see more people come in with breathing difficulties in the coming days.

"As the fires die down and people start going out, there will still be lots of dust and ash in the air," Stringer said.

Health experts say the most dangerous byproducts of wildfires are the fine particles that are not visible to the naked eye. The particles can flow into the lungs and worsen symptoms of asthma, bronchitis and emphysema.

In addition to the public warnings, health officials urged schools to cancel outdoor sports activities until the air improves.

The Los Angeles Unified School District, the nation's second largest with more than 708,000 students, suspended all outdoor activities Tuesday.

Hospital staff at Mountains Community Hospital in the resort town of Lake Arrowhead helped several travelers refill their oxygen tanks "to give them a peace of mind," said Susan Lowell, the hospital's director of patient care services.

The hospital also decided to open its kitchen and offer food to travelers who needed a break just like it did in 2003 when the area was besieged by the devastating Old Fire.

—Associated Press