LOS ANGELES - Business was brisk at Teddy’s Cocina in Pasadena as wildfire evacuees ate lunch and passers-by ducked indoors to escape from the brown, smoky air blanketing the city.

“It’s not breathable,” said Ms Dulce Perez, a cook at the restaurant, as an eye-watering haze hung overhead on Jan 9 about 3.2km away from one of the multiple fires burning around Los Angeles. “We just try to stay indoors.”

This week, as the wildfires raged and smoke billowed across Los Angeles, officials issued air quality alerts, schools cancelled classes and scientists warned about the dangerous - even fatal - consequences of wildfire smoke.

All around the United States’ second-largest city, residents worried about air that has, at times, turned lung-burning from the ash, soot and smoke emanating from fires that have destroyed 10,000 structures.

Air purifiers were sold out at some big-box stores, according to interviews with employees at four businesses.

Some residents were taping windows to keep the smoke out of their homes. And Los Angeles officials urged people to stay indoors in areas where smoke was visible.

While conditions improved on Jan 10, an air quality alert remained in effect until the evening and dangerous particulate matter remained around four times World Health Organisation guidelines.

At the Pasadena Convention Centre, which has been converted to a temporary shelter, aid workers from Sean Penn’s global humanitarian organisation, Core, were handing out N95 masks on Jan 10.

Emergency response programmes manager Sunny Lee said the homeless were particularly vulnerable to bad air.

“There was no place for them to go inside, and so they were suffering even more outside with the poor air quality, without any kind of masks,” said Ms Lee. “So, we pushed out N95 to our partners that reached those communities. We’re distributing as many as we can.”

Fanned by fierce winds and fuelled by vegetation bone-dry after a long period of little or no rain, the Los Angeles fires broke out on Jan 7 and have relentlessly burned more than 13,760ha, or some 137sq km.