Fire Information Officer Michaela Swan says the wildfire grew aggressively overnight due to strong winds, and is now estimated to have burned about 8.5 square kilometres.
Swan says the fire has now moved into an accessible area that may give the nearly 80 firefighters battling the blaze the ability to get the upper hand.
She says they're using heavy machinery, air tankers, five helicopters and fire retardant to try to contain and stop the fire.
She says investigators are looking into the cause of the blaze, which is believed to have been started by human activity.
While investigators don't yet know how the fire was triggered, Swan says investigators have ruled out natural causes such as lightning strikes.
It's a serious fire that crews have been battling for weeks, she adds — compounded by a lack of rain in the area.
Swan says the area is a sparsely-populated with ranches and it's not yet known how many homes will be subject to the evacuation.
There was some confusion earlier about whether or not residents would be forced to comply with the evacuation alert — Swan had said the evacuation was mandatory, while a spokesperson with the Thompson-Nicola Regional District had said it was voluntary.
A high fire-danger rating has been issued for the entire Okanagan, from Osoyoos to Vernon and the Shuswap.
Swan is reminding the public to be vigilant whenever they have open campfires, and asking smokers to be careful about how they dispose of cigarettes.
Note to readers: This is a corrected story. A previous version wrongly said the evacuation is mandatory