The fire broke out at Hay Kingdom near Winters, about 20 miles from Vacaville, just before midnight.
Firefighters expect it to burn for at least a day or more. Dixon, Davis, Woodland, Sacramento and Vacaville fire departments are fighting the fire.
People reported seeing it all the way from Fairfield and smoke from the fire has impacted the air quality in the South and East Bay.
There is no word yet was sparked the blaze or if there are any injuries.
