Fire crews have been working long days dousing small hot spots like this one as they try to contain the larger wildfires raging across British Columbia. (CBC)

Wildfires in British Columbia's Cariboo region are eating up huge tracts of timber and the province's firefighting budget with it, officials say.

Three clusters of fires in the north-central Interior region are now estimated at up to 500 square kilometres, fire officials say.

Two groups of fires in the Williams Lake area — the Meldrum Creek complex and the Alexis Creek cluster — have a combined size of 350 square kilometres, while the Pelican Lake cluster southwest of Prince George covers about 150 square kilometres.

The fires are being fuelled by hot, dry conditions, combined with wind and lightning, and are being fought by hundreds of ground crews aided by water bombers and helicopters.

B.C.'s battle against forest fires has already consumed the province's entire $52-million firefighting budget, with an estimated 400 fires still burning. The province is currently spending upward of $6 million a day as it wrestles with more than 400 wildfires.

About 90 active fires in B.C. are larger than 10 hectares. Almost two dozen of those fires are considered fires "of note," because of their visibility or potential threat to public safety.

Officials expect an average of 50 new fires a day to break out unless heavy rain develops, and that's not in the current forecast.

The fire situation has severely disrupted the plans of motorists travelling between B.C. and the Yukon. Highway 37 has been closed since last week because of an 11,000-hectare fire that shows no signs of being contained.

Air tankers have been flying long hours as they battle fires such as this one near Spotted Lake in Osoyoos, B.C., earlier this week. (Chris Phillips/Canadian Press)The B.C. government has deployed trucks and even a helicopter to escort a few travellers along the smoky road when conditions permit, but fire information officer Lindsay Carnes says motorists shouldn't count on that kind of help.

"If the fire behaviour or the visibility isn't conducive to opening the highway, then the highway doesn't open," Carnes told CBC News.

The only other option for drivers is Highway 97, which boosts travel time by at least two hours. Carnes urged motorists to contact the DriveBC website for the latest travel information.

Some residents refuse to leave

Evacuation orders are in effect in four areas in the Cariboo, but officials are frustrated by some residents' refusal to leave.

In the Meldrum Creek area west of Williams Lake, dozens of residents have decided to defy the order to leave and are staying put.

Eric Reay, a cattle rancher, is one of those who aren't leaving home, even though a wildfire is burning less than half a kilometre from his spread.

"My wife left and she stays with our son, and I just stay home and look after the cat and the rest of the animals and make sure that everything is all right," he said.

Last year, B.C. budgeted $60 million to fight forest fires but ended up spending $400 million as more than 2,000 wildfires swept through the province.

The B.C. Wildfire Management Branch reports 1,235 fires have been recorded so far this fire season, with 84,307 hectares burned.

With files from The Canadian Press and the CBC's Jeff Davies and Sarah Towle