Nearly 10,000 people were evacuated and a state-wide emergency declared Friday as a wildfire ripped through parts of Reno, Nevada, officials and reports said.

Residents who did not immediately have to evacuate were told to stay indoors after smoke engulfed the area, and as some 450 firefighters battled to contain the 2,000-acre (810-hectare) Caughlin Fire in southwest Reno.

"Crews from multiple fire response agencies are working diligently to fight the fire," the city fire department said, adding: "Air quality readings throughout the valley are elevated regionwide."

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Some 9,500 people had so far been evacuated as Nevada state, Washoe county and Reno city authorities all declared a state of emergency, Reno said on its official website.

The Reno Gazette-Journal reported that 25 houses had been affected by the blaze, but cited fire officials saying that 4,900 homes were potentially threatened in the fire area.

Reno Fire Chief Mike Hernandez declined to speculate on what caused the fire or where it started, according to the newspaper.