The Squamish-Lillooet Regional District says the alert is not an order to evacuate but an advisory requesting residents be prepared to leave the area on short notice.
The Ministry of Forests says the blaze was sparked by lightening and was discovered on Monday about seven kilometres southeast of Pemberton and south of Lizzie Creek.
Air tankers were called in Tuesday to assist ground crews and cool the fire's behaviour.
By Wednesday evening, 46 firefighters and six helicopters were battling the flames.
The ministry says no homes or structures are currently being threatened, and no roads are closed in the area.
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