Residents in the San Francisco Bay Area have been urged to seal themselves in their homes as smoke spreads from a growing wildfire in mountains to the east.
The Morgan Fire has scorched 3,718 acres in just three days and is 45 percent contained, a Cal Fire spokesman told NBC News early Tuesday.
A smoke warning issued by the Bay Area Air Quality Management District (BAAQMD) advised people in the populated region to stay indoors and shut their windows as smoke moved southward.
The blaze, in Mount Diablo State Park southeast of Clayton, threatens 100 buildings and has prompted local schools and community groups to keep their activities indoors, NBC Bay Area reported.
Some 700 firefighters are battling to contain the fire, aided by four air tankers, 11 helicopters and 100 fire engines. When the fire started Sunday, some areas of the 11,000-strong community of Clayton were ordered to evacuate by Cal Fire, although speaking Tuesday the fire service could not give exact numbers.
It is just the latest front in California’s summer-long firefight. The most significant of these blazes is the colossal Rim Fire in the Yosemite National Park which has grown to almost a quarter of a million acres and is the third biggest in the state's history.
The BAAQMD issued an official smoke warning late Monday urging people -- especially those with asthma or other types of lung disease – to stay inside their homes.
“If you have heart or lung disease, if you are an older adult, or if you have children, talk with your doctor about whether and when you should leave the area,” the BAAQMD statement said. “Reduce exposure to smoky air by remaining indoors with windows and doors closed.”
Meanwhile, a wildfire in Shasta County in the northern part of the state has damaged 30 structures, many of them homes, and is threatening another 350 structures.
The wind-whipped Clover Fire, near the rural community of Happy Valley, has grown to more than 11 square miles.
State fire spokeswoman Teresa Rea says the blaze began around 1 p.m. Monday and quickly burned through grass and oak. Happy Valley is about 150 miles north of Sacramento.
Rea says fire crews did make good progress against the blaze overnight, raising containment from 5 percent to 40 percent. More than 1,100 firefighters are battling the blaze. The cause is under investigation.
NBC News’ Simon Moya-Smith and Daniel Arkin and The Associated Press contributed to this report.