Firefighters were battling the quickly growing "Silver Fire" between Banning and Idyllwild, which was estimated at 5,000 acres after starting earlier Wednesday afternoon.
The surrounding mountain communities of Poppet Flats, Twin Pines and Silent Valley were given mandatory evacuations, according to the Riverside County Fire Department. The fire was first reported at 2:05 p.m.
The wildfire was "burning at a critical rate," the department said.
"This has been a very fast-moving wildfire throughout this afternoon," Cal Fire's Daniel Berlant told KPCC. "Right now we have a number of homes that are being threatened."
One firefighter was injured, and several structures were consumed by the fire. A civilian was also injured, according to the department, but the extent of that injury was unknown.
Firefighters are also still dealing with the Falls Fire, which is at 73 percent containment. Some resources from that fire were already in the process of being released, and more were being shifted to the Silver Fire, as its nature makes it a higher priority, Berlant said.
Firefighting resources are being moved from Central California to the area to help defend structures, Berlant said.
The Silver Fire is about 20 miles from where the Mountain Fire started — which burned 43 square miles last month.
Michelle Williams, an employee at Stage Coach RV Park in Banning, told KPCC that the highway patrol is closing down roads nearby.
"We can see a lot of smoke from the back area of our campground, and there's a lot of traffic out front, and they're stopping everybody from going up the mountain," Williams said.
KPCC's Nick Roman spoke with Christina Hernandez, a reporter at Redlands Daily Facts, who's currently at the command post for the Silver Fire. She said she could see tractors and other machinery headed toward the fire, along with the firetrucks and air support.
"It's just kind of a crazy scene out here. There's lots of fire trucks. There's residents hanging out outside Banning High School waiting to see if they can go up to their homes."
Highway 243 between Banning and Azalea Trail is closed.
The fire department deployed 450 firefighters, 14 fire crews, 71 fire engines, five helicopters, four airtankers, three water tenders and three bulldozers, according to the department. The resources fighting this fire include a DC-10 airtanker that was moved off of dealing with other fires.
Evacuation centers have been set up at Hemet High School and Beaumont High School. Animals can be taken to San Jacinto Valley Animal Campus.
This map shows the location of the Silver Fire:
This story has been updated.