The fast-moving brush fire that has scorched more than 13,000 acres outside Reno, Nevada, since erupting Saturday was caused by human activity, authorities said.
Firefighters have yet to contain any part of the blaze, which is threatening roughly 1,000 homes and has prompted evacuations for roughly 42,000 residents.
Nevada Gov. Joe Lombardo declared a state of emergency for Washoe County as the Hawk Fire grew quickly throughout the day. Strong, gusty winds, low humidity and dry vegetation helped fuel the flames, according to the Truckee Meadows Fire Protection District.
About 400 firefighters and other personnel from local, state and federal agencies were working the fire Saturday night, both on the ground and from the air. Three helicopters were set to fly overnight as crews worked to protect homes and other property.
"The Hawk Fire is a very dynamic incident for us as it's being driven by the winds," Truckee Meadows Fire and Rescue Chief Richard Edwards said in a video posted to social media.
"The wind-driven fires move very rapidly into our residential areas, creating a lot of challenges for our firefighters to save homes and protect lives," Edwards added.
Officials ordered new evacuations for the Somersett community, including areas north of Somersett Parkway to Robb Drive, as well as neighborhoods north of West 7th Street to North McCarran Boulevard.
About 1,000 homes were also in a "Warning — GET SET" zone, with residents told to be ready to leave.
Reno Mayor Hillary Schieve urged anyone ordered to evacuate not to wait, saying the fire had already damaged structures.
"If you have been told to evacuate, please don't wait!" Schieve said in a statement. "Structures have already been burned in this fire and your life is more important than a building."
The mayor did not immediately specify what kind of structures were burned. She said leaving before the fire arrives also allows firefighters to focus on battling the flames rather than rescuing people who stayed behind.
Lombardo also said the fire was threatening homes and other structures.
"This is an active and rapidly evolving situation, and I urge everyone in the affected areas to remain vigilant and follow the direction of local officials," the governor said in a statement.
Officials were also keeping a close eye on the fire near a Washoe County correctional facility.
Washoe County Sheriff Darin Balaam said his office was working with fire and emergency crews and was prepared to act if conditions changed.
"The safety and security of every incarcerated individual, as well as our staff, remains a top priority," Balaam said. "We will continue to evaluate conditions and respond accordingly."
The Associated Press contributed to this report.