By David Ljunggren

OTTAWA (Reuters) -Wildfires spread in the western Canadian province of British Columbia on Friday, while in the east, Quebec said it would start efforts to control blazes that have sent smoke billowing across North American cities.

Canada is enduring its worst start to the wildfire season, with 2,392 fires so far this year and 4.4 million hectares (10.9 million acres) burned, according to the Canadian Interagency Forest Fire Centre (CIFFC), roughly 15 times the annual average over the last decade.

The CIFFC reported 427 active fires, of which 232 were out of control.

Around 2,500 people were told to evacuate the community of Tumbler Ridge in northeastern British Columbia on Thursday. Officials also expanded evacuation orders for the Donnie Creek fire, the second-largest recorded in the province.

In the eastern province of Quebec, forestry minister Maite Blanchette Vezina said that as extra resources arrived, authorities would be better able to control the fires. Hundreds of firefighters from across the world have flown to Canada.

"This sprint phase is over - now we're in a marathon phase. So in the next days and weeks we will be working to contain those active fires to bring them under control and eventually extinguish them," she told a briefing.

"We also hope the weather will cooperate. Some precipitation is expected in some areas, but in the next few days the situation will remain critical."

Earlier, fire fighters contained blazes that had threatened hydro-electric facilities in the Lac-Saint-Jean area, about 300 km (190 miles) north of Quebec City, public broadcaster Radio-Canada said.

Federal authorities said this week they were concerned by the threat that blazes could pose to critical infrastructure.

Temperatures in parts of British Columbia soared to more than 30 degrees Celsius (86 Fahrenheit) this week, nearly 10 degrees above the seasonal average. While rain is expected over the weekend there is a risk of lightning strikes.

Although wildfires are common in Canada, it is unusual for blazes to be burning simultaneously in the east and west, stretching resources and fuelling concerns about the worsening consequences of climate change.

In the western province of Alberta, more than 3,500 people remain under evacuation orders and heat warnings were in effect over much of the central area.

Wildfire smoke continued to plague millions of people across eastern Canada and the northeastern United States.

Poor air quality is expected to persist in cities including Ottawa, Toronto, New York and Washington until Sunday when the wind direction shifts.

Nearly a third of the fires burning across Canada are in Quebec, more than any other province. Rain is expected in Quebec and neighbouring Ontario on Monday.

(Additional reporting by Ismail Shakil in Ottawa;Editing by Stephen Coates, Jane Merriman and Chris Reese)