The wildfire was first reported at about 3:50 a.m. Sunday near the 200 block of North Crystal Springs Rd., about four miles northwest of the city of St. Helena.
RELATED: 2 additional fires reported near Glass Fire in North Bay, mandatory evacuations underway
Almost 900 firefighters from numerous local fire departments and CAL FIRE are working the fire. Officials say air tankers are helping in the fight when conditions permit.
CAL FIRE added overnight firefighting crews will work on perimeter control, defending structures and evacuation planning.
PHOTOS: Striking photos capture crews battling Glass Fire burning thousands of acres in Napa County
Firefighters said hot temperatures and low humidity, combined with erratic winds, should make fighting the Glass Fire difficult.
Bay City News contributed to this report.
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