A B.C. wildfire raging west of Prince George continues to spread and now covers an estimated 13,000 hectares, up from 8,000 the day before, officials said Thursday.

B.C. Wildfire Management Branch officials said fire crews battling the Little Bobtail Lake fire noticed "an increase in fire activity overnight" Wednesday.

"Relative humidity numbers continue to be very low," the B.C. Wildfire Management Branch reported. "This, along with dry conditions, are challenging suppression efforts. Daily forecasts indicate that temperatures are expected to be in the mid-20s.

"Smoke is very visible from the highway and nearby communities."

An estimated 80 people have been removed so far from the area, about 60 kilometres southwest of Prince George, and others have been advised to prepare to leave.

No structures have been damaged.

On Wednesday, B.C. Parks closed and evacuated Dahl Lake Provincial Park and Bobtail Mountain Provincial Park.

More than 100 firefighters, five helicopters and 10 pieces of heavy equipment have been working around the clock to try and contain the wildfire.

Crews are also supported by four Air Tractor AT-802F "Fire Boss" amphibious airtankers that can drop water, foam or retardant on the fire.

"Additional ground, air and equipment resources will be added to the fire to slow the rate of spread," the B.C. Wildfire Management Branch said. "All resources will work to establish containment lines on the fire (Thursday)."

The fire was reported May 8 and fire crews responded the next day.

The cause of the wildfire is under investigation.