Reno Fire Chief Michael Hernandez said more than 230 firefighters were battling the blaze, which had grown to nearly 5 square miles within hours.
Hernandez confirmed "several" homes had been destroyed. He said he didn't know the exact number but told reporters "the news is not good."
There were no immediate reports of any deaths or injuries.
A Reno television station reported at least 10 homes had burned since the fire broke out about 12:45 p.m. along U.S. Highway 395.
Washoe County officials declared a state of emergency a few hours later, and Gov. Brian Sandoval followed with a statewide declaration.
A five-mile stretch of U.S. 395 was closed as the strong winds pushed the flames north toward Reno along the base of the hillsides, Washoe County sheriff's Deputy Armando Avina said. Heavy smoke reduced visibility to zero.
By nightfall, the fire had burned to the city's southern outskirts. Flames were visible 10 miles away in the downtown casino district.
"It's moving at a very fast rate," Avina said. "The winds are extremely powerful in this area."
The winds died down after nightfall and rain started falling, much to the delight of fire crews.
Deputies went door to door asking people to leave their homes in Pleasant Valley, Old Washoe Valley and Saint James Village, Avina said. They evacuated about 300 students from Pleasant Valley Elementary School.
Erika Minnberry, 28, said she didn't become concerned at first because smoke from the fire appeared far enough away.
"Probably 30 minutes later, it was up to our house because of the high winds," she said. "I felt pure survival adrenaline. When we drove away, the smoke was so thick, we could barely see ahead of us. Now I feel anxiety. I couldn't find my two cats at the time and I hope they're OK."
KRNV-TV reported that 10 homes had burned, including a half dozen in the Washoe Valley Estates neighborhood. The Reno Gazette-Journal reported explosions could be heard in the area.
Firefighters had zero containment of the blaze and were concentrating on using crews and trucks to protect homes in the path of the flames, Hernandez said.
He estimated firefighters had saved about 1,000 structures and said another 80 to 120 firefighters were expected to arrive on scene before midnight.
"To say we are in the thick of battle is an understatement," he told reporters.
Martinez said the fire was "almost a carbon copy" of a huge wild fire on the edge of the Sierra foothills that destroyed 30 homes in southwest Reno in November.
"It is a wind-driven event and a combination urban-wildland fire," he said.
Like in that fire, Martinez said, strong winds and dry conditions helped fuel the latest blaze. The Reno area had gone a winter-record 56 days without any precipitation until light snow fell earlier this week.
More wet weather was forecast Friday, and snow was forecast Friday night. But high winds were expected to continue, with gusts up to 40 mph.
The strong winds that blew over the Sierra ahead of the winter storm caused delays earlier Thursday in Vice President Joe Biden's visit to Reno, where he was two hours late to give a speech at Galena High School on the south end of town.
The air smelled of smoke at the school, which sits on the Mount Rose Highway leading to Lake Tahoe. Biden told the audience about 25 minutes into his speech that he was cutting his remarks short because of the fire.
Martinez conducted his 5:15 p.m. briefing at the high school, which was evacuated along with surrounding neighborhoods shortly afterward.
The flames, up to 40 feet high, raced through sage brush, grass and pines in an area where small neighborhoods are dispersed among an otherwise rural landscape. Washoe County animal services officials were helping round up horses and other livestock for evacuation.
The American Red Cross opened an evacuation center at Damonte High School, where the children from the elementary school were taken.
Trooper Dan Lopez said U.S. 395 was closed from the south end of Reno at Mount Rose Highway, or state Route 431, to the north end of Washoe Valley near the Bowers Mansion. Northbound traffic was being rerouted back to Carson City about 15 miles to the south.
Winds gusts of up to 82 mph were reported within a few miles of the fire, and a gust of 122 mph was recorded atop Slide Mountain, which is between the fire and Reno at the Mount Rose ski resort.
Associated Press writers Martin Griffith in Reno and Sandra Chereb in Carson City contributed to this report.