Nov. 15 (UPI) -- As crews get a better handle on the wildfires in California, toxic smoke from the flames is creating hazardous conditions for hundreds of miles, officials say.
The Camp Fire forced schools and universities to close Thursday in the Bay Area as the smoke raises concerns for children or people with lung conditions.
The fire, north of San Francisco, has so far killed at least 56 people and has burned more 140,000 acres and 8,700 homes, Cal Fire said Thursday. It's 40 percent contained.
Health officials warned people in the Los Angeles Basin, the Central Valley and San Francisco Bay Area to avoid exercising outside and wear protective masks, particularly if they have asthma or other breathing problems.
New N95 masks are recommended and should be worn tightly to shut out the smoke.
San Francisco State, Cal State East Bay and San Jose University were among the schools that canceled classes Thursday. Many will be closed through the weekend as the Camp Fire rages in Butte County.
Several public schools reopened in the Bay Area on Thursday, raising concerns among parents. Many children walked to school wearing masks. Some schools canceled recess and outdoor activities.
The smoke has also caused flight delays at San Francisco International Airport with 10 percent of flights delayed.
In the Los Angeles area, the Woolsey Fire has killed two people, destroyed more than 500 homes and burned nearly 100,000 acres, Cal Fire reported. It's 57 percent contained.
The Hill Fire in Ventura County is 97 percent contained, Cal Fire reports. The fire burned 4,531 acres and destroyed two homes and damaged two.
President Donald Trump is set to visit California on Saturday to meet with people affected by the fires, the White House announced Thursday.
Trump previously criticized California for its handling of past wildfires and forest management, and threatened to cut funding to the state.
"There is no reason for these massive, deadly and costly forest fires in California except that forest management is so poor," Trump said in a tweet last week. "Billions of dollars are given each year, with so many lives lost, all because of gross mismanagement of the forests. Remedy now, or no more Fed payments!"
On Monday, Trump issued approved a request by Gov. Jerry Brown for a major declaration, which Brown said "provides a wide range of federal assistance programs for individuals and public infrastructure, including funds for both emergency and permanent work."