A fast-moving fire in northeastern B.C. grew significantly overnight and is bearing down on two oil-and-gas workers' camps in the area.

The Red Deer Creek fire burning southeast of the mining community of Tumbler Ridge was caused by a lightning strike on Sunday and now covers 5,000 hectares, or about 50 square kilometres.

Jillian Kelsh of the Wildfire Management Branch says the fire is igniting the tops of trees and burning near oil-and-gas wellheads and that camps consisting of about 200 workers remain evacuated.

She says the fire is expected to double in size because of hot, dry and windy conditions, and there's no rain in the forecast.

The branch reports that 120 firefighters, five helicopters, four air tankers and two pieces of heavy equipment are tackling the flames, but  Kelsh says the number of firefighters is expected to increase.

Kelsh says one of the biggest concerns is that the blaze may cross into Alberta.

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The Red Deer Creek Fire has not been contained and is expected to double in size due to more hot, dry weather in the forecast. (B.C. Wildfire Management Branch)