REDDING — The ferocious Carr Fire that ripped into this city of 90,000 after winds blew it over the Sacramento River has taken the life of a second firefighter, destroyed 500 structures and prompted authorities to expand evacuations Friday.

The intensity of the heat created fire whirlwinds that uprooted trees and turned over cars as 37,000 residents fled for their lives after the fire entered the northwest side of the city late Thursday night.

Three people were missing — two young children and their great-grandmother, who were last known to be at a home that was leveled by the fire, a family friend said.

“This fire is a long way from being done,” Cal Fire Chief Ken Pimlott said at a news conference. “We’re seeing fire whirls — literally what can be described as a tornado. ... These are extreme conditions. This is how fires are burning in California. We need to take heed. Evacuate. Evacuate. Evacuate.”

By Friday night, 48,000 acres had burned and only 5 percent of the blaze was contained. Five hundred structures were destroyed and 75 damaged, Cal Fire Shasta-Trinity Unit officials said.

All day Friday, relatives of Emily Roberts, 4, and her 5-year-old brother, James, and their 70-year-old great-grandmother, Melody Bledsoe, searched in hospitals and shelters for their missing loved ones.

Bledsoe was caring for the children in Redding, said Donald Kewley, the boyfriend of Bledsoe’s granddaughter, Shelley Hoskinson. Kewley, who lives 2 miles from Bledsoe’s house, said he was standing on the roof of his home on Thursday night as the Carr Fire raced closer and closer. He said he called Bledsoe’s house.

“She was screaming, ‘It’s getting closer,’ and you could hear the sirens,” Kewley said.

He tried to drive to Bledsoe’s house near Quartz Hill and Keswick Dam roads, about 2 miles north of downtown Redding, but could get no closer than about a half mile before flames forced him to turn around.

“You could see a 50-foot wall of flames, moving fast,” he said.

On Friday, Kewley and Bledsoe’s husband, Ed, went to the area where the home had been.

“It looked like a bomb went off,” said Donald Kewley, “We went back there and the whole neighborhood is gone. It’s absolutely obliterated. It’s just a smoldering mess.”

The family posted pictures of the missing family members on social media, including photographs of the two children in their Halloween costumes.

“Please help,” the family’s post said.

In the early evening, Shasta County Sheriff Tom Bosenko said no reports of missing persons had been received, but “we expect there will be missing person reports, and perhaps unreported deaths that we are unaware of” at the moment.

With temperatures exceeding 100 degrees and the terrain dry, authorities said the fire will burn for days.

“We’re seeing fire conditions like we’ve never seen before, making this really quite an event to stay out in front of,” said state Office of Emergency Services Director Mark Ghilarducci.

Among the buildings that burned were the 1920s schoolhouse at Shasta Historic State Park, west of Redding, officials said. The brewery and cemetery in the historic area were damaged, but officials removed artifacts for safekeeping, according to Gloria Sandoval, a spokeswoman for California State Parks.

Gov. Jerry Brown declared a state of emergency in Shasta County and requested federal aid on Friday.

“I am requesting Direct Federal Assistance, including Department of Defense air assets to immediately mitigate the impacts of this fire; shelter supplies and water for 30,000 evacuated residents in Shasta County; U.S. Department of Agriculture’s assistance in evacuating large animals; mass care; evacuation assistance for individuals with access and functional needs; and ambulatory transport,” Brown said.

The two firefighters killed battling the Carr Fire were a contract bulldozer operator who died Thursday whose name was not released, and Jeremy Stoke, a fire inspector with the Redding Fire Department.

The deaths bring to three the number of firefighters who have died this month battling wildfires in the state. Braden Varney died fighting the Ferguson Fire near Yosemite National Park on July 14 when his bulldozer rolled over.

The fire also caused injuries to firefighters and residents, officials said.

Among those injured were three Marin County firefighters who suffered burns to their ears, face and hands. Two were treated and released, while the third was transported to UC Davis Medical Center, said Battalion Chief Bret McTigue, of the Marin County Fire Department.

“A sudden gust of wind pushed the fire forward ahead of the fire front, and they received severe heat lash from adjacent pine trees,” McTigue said.

The injured firefighters were identified as Scott Pederson, 37; Tyler Barnes, 34; and Brian Cardoza, 26 — department veterans for 19 years, four years and three months, respectively.

The Carr Fire began Monday after a vehicle mechanical failure near Whiskeytown, about 30 miles west of Redding, Cal Fire officials said.

The blaze is one of more than a dozen wildfires across California.

Northwest wind gusts of up to 25 mph were expected Friday evening in the canyons near the fire, he said.

Driving through Shasta County, Cal Fire spokesman Scott McLean said he saw large and small trees that had been ripped out of the ground and fallen onto homes. One gust blew out the windows of a Cal Fire pickup truck, he added.

“That tells me there was a heck of a lot of erratic winds,” McLean said. “That’s what these firefighters are having to deal with.”

There are 1,748 fire personnel responding to the conflagration, including 110 engines, 34 water tenders, 10 helicopters, 51 hand crews and 22 bulldozers.

An evacuation center was available at Shasta College and Weaverville Elementary School.

Chronicle staff writers Lauren Hernandez, Sarah Ravani and Nanette Asimov contributed to this report

Trisha Thadani, Melody Gutierrez and Steve Rubenstein are San Francisco Chronicle staff writers. Email: tthadani@sfchronicle.com; mgutierrez@sfchronicle.com; srubenstein@sfchronicle.com.