A hay fire at Moreda Valley Dairy west of Petaluma burns at dawn on July 20, 2016. (Courtesy of the Wilmar Fire Department)
Updated at 2:45 p.m. Wednesday, July 20:
Members of at least six fire agencies are battling flames at a dairy farm west of Petaluma that is burning an estimated 400 tons of alfalfa hay and is expected to take several days to put out.
The fire at Moreda Valley Dairy on Chileno Valley Road in the Wilmar area near the Sonoma-Marin County border started around 2 a.m., fire officials said.
"It's quite a large fire and it's not something that goes out really easy," said Mike Mickelson, chief of the Wilmar Fire Department. "We're expecting it to put smoke out for quite a while."
The fire is technically contained but firefighters are expected to work to extinguish it for the next two to three days, said Brentt Blaser, a Sonoma County Fire and Emergency Services spokesman.
The smoke from the fire stretched from the Petaluma Valley to the northern edge of Novato, Mickelson said.
Winds from the west are expected to increase from 10 to 20 mph in that area this afternoon and could send smoke eastward, said National Weather Service forecaster Steve Anderson.
Concerns over the smoke have prompted the Wilmar Fire Department to advise people not to call 911 unless they see active fire or have another emergency, according to a message posted on the agency's website.
Local air district officials are looking into the blaze. The Bay Area Air Quality Management District sent an inspector to the area, according to agency spokeswoman Lisa Fasano.
The district advised residents who live and work near the fire to close their windows and doors and set their air-conditioning units on "recirculate" to prevent smoke from being drawn into their homes and businesses.
People with respiratory conditions who feel impacted by the smoke should move to an area that is upwind or outside the smoke path until the smoke dissipates and the fire is out, Fasano said.
The fire, which is under investigation, did not injure anyone.
Along with the Wilmar Fire Department, firefighters with the Sonoma County, Marin County, Rancho Adobe and Lakeville fire departments, as well as Cal Fire, are on scene.
Moreda Valley Dairy is a large operation. Hundreds of cows at the facility were not near the hay storage facility that caught fire, Mickelson said. A company representative did not immediately return a call for comment.
"One of the concerns is that it's right next to rolling hills, and if an ember gets on that we'll have a vegetation fire," Mickelson said.
This report was updated to include comments by a Bay Area Air Quality Management District representative.