A raging wildfire that has prompted a state of local emergency and forced evacuations on south-central Vancouver Island has grown to span more than 20 square kilometres as it displays some of the most severe kinds of fire behaviour.

The British Columbia Wildfire Service says the blaze, located about 12 kilometres south of Port Alberni, is burning at rank four and five on a six-point scale, meaning "extremely vigorous" flames are consuming trees from trunk to canopy.

Videos posted on social media show the Mount Underwood wildfire lighting up a slope and billowing thick plumes of smoke, while helicopters dump water on the flames.

The fire discovered on Monday has spurred the Alberni-Clayoquot Regional District, City of Port Alberni and Tseshaht First Nation to declare states of local emer

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