Updated

Reno Fire Chief Michael Hernandez says more than 4,000 people have been evacuated and hundreds of firefighters remain "in the thick of battle" as a wind-driven wildfire burns across thousands of acres toward the city's southern border.

Hernandez says more than 230 firefighters are battling the blaze that had grown to nearly 5 square miles by 5 p.m. Thursday.

Hernandez confirmed homes had been destroyed. He said he didn't know how many but told reporters "the news is not good."

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 about 10 miles south of Reno.

Hernandez estimated firefighters had saved about 1,000 structures. He says another 80 to 120 firefighters are expected to arrive on scene before midnight.

Gov. Brian Sandoval has declared a state of emergency.

Winds gusting up to 82 mph pushed a fast-moving brush fire through a valley south of Reno on Thursday, burning several homes, threatening dozens more and forcing hundreds of residents to evacuate their neighborhoods.

The blaze was burning about 15 miles from the downtown Reno casino district and within about five miles of the southern city limits.

A Reno television station reported 10 homes had burned, but city spokesman Chris Good said the situation was still too chaotic and hectic to offer any estimates.

"I don't have the number of acres, I don't have the number of homes, I don't have the number of firefighters," Good told The Associated Press.

There were no immediate reports of any deaths or injuries.

Washoe County declared a state of emergency shortly before 4:30 p.m., about four hours after the fire broke out along U.S. Highway 395.

A five-mile stretch of the highway 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.

"It's moving at a very fast rate," Avina said. "The winds are extremely powerful in this area."

Authorities shut down about a five-mile stretch of U.S. 395 after heavy smoke reduced visibility to zero north of Washoe Lake in Pleasant Valley.

Deputies were going 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.

Ten homes had burned — a half dozen of them in the Washoe Valley Estates neighborhood, KRNV-TV reported. The Reno Gazette-Journal reported explosions could be heard in the area.

Firefighters were concentrating on using crews and trucks to protect homes in the path of the flames.

The strong winds blowing over the Sierra ahead of a 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, which broke out about 12:45 p.m.

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.

The conditions were similar to those Nov. 18, when a wind-driven fire destroyed 30 homes in southwest Reno.

National Weather Service forecasters were predicting the storm would bring rain to the area Thursday night before turning to snow Friday night. High winds were expected to continue, with gusts up to 40 mph.

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Associated Press writer Sandra Chereb in Carson City contributed to this report.