VANCOUVER -- Smoke from wildfires in British Columbia has forced some people to visit hospitals because of breathing problems and chest pain, says the provincial health officer.

Dr. Perry Kendall said emergency rooms in Whistler and Burnaby have seen a slight uptick in patients dealing with respiratory conditions during an early fire season.

He said about 12 people have been to hospital in the resort town of Whistler, and another 25 to 30 people have visited hospitals in the Fraser Health region, which extends from Burnaby to Hope.

Thick smoke has been drifting south to Whistler from a 200-square-kilometre blaze near Pemberton. It's among about wildfires currently burning throughout B.C.

Kendall said the numbers of people ending up in hospital was low considering the amount of smoke permeating the province.

"I think the numbers are relatively low because I think people are taking advice and are not exposing themselves to the fine particle pollutants in the air," he said Thursday.

Officials have advised people, especially the elderly and those suffering from chronic conditions, to avoid strenuous activity outdoors because of poor air quality.

But the smoke didn't seem to be keeping adventure seekers out of Whistler Blackcomb's mountain bike park.

"Our riders who are here to ride the bike park continue to ride," said David Macfarlane, director of operations at Whistler Blackcomb. "The numbers were down a bit just because it was tough conditions. But they're still out there riding today and right now."

Macfarlane said staff were advising visitors about the high-risk air quality advisory after part of a kids' mountain biking camp was held indoors instead.

On Wednesday, residents in part of the Cariboo region were forced from their homes after a wildfire more than doubled in size.

Fire information officer Emily Epp said Thursday that the blaze in the Puntzi Lake area, about 180 kilometres west of Williams Lake, had grown to about 12 square kilometres in size.

Thirty properties have been evacuated, and other residents are on alert to leave their homes at any moment.

Chief fire information officer Kevin Skrepnek said there have been 945 fires throughout the province since April 1, burning more than 2,300 square kilometres of land.

Over 600 contractors have joined provincial fire crews to battle the blazes.

Their numbers have been bolstered with help from 100 Ontario firefighters and two water-skimming aircraft, which can also drop fire retardant. Crews from Australia were set to join the effort next week.

Forests Minister Steve Thomson said the province has signed a one-month contract to use the Martin Mars air tanker at a cost of $600,000 a month, plus hourly flying costs.

The aged water bomber has not been used to fight forest fires in B.C. for the past two years, but Thomson said the aircraft is an important tool during the unpredictable fire season.

A Port Alberni-based company that owns the tanker said it can drop 27,000 litres of water at once.