Smoke from hundreds of wildfires blazing across British Columbia has prompted the extension of air quality advisories across most of the central and southern area of the province.

Health advisories will remain in place until at least Friday evening, Metro Vancouver authorities announced Thursday morning.

"We did get a bit of rain overnight on the North Shore but it didn't help all that much. We're hoping to clear things out by the weekend," Laurie Bates-Frymel, Air Quality Planner for Metro Vancouver, told

On the south coast, only the Greater Victoria region has escaped health advisories related to deteriorating air quality.

Residents in Vancouver, the Fraser Valley and the Sea-to-Sky corridor were added to the advisory list yesterday, joining those in Prince George, Quesnel, Williams Lake, Kamloops and the entire Okanagan Valley.

Williams Lake had the highest reading Thursday on the Air Quality Health Index scale, which measures relative health risks from air pollutants. The central B.C. town scored a whopping 19 on the normally 10-point scale.

Bates-Frymel says the fires have sent particulate matter, or fine soot, into the atmosphere.

"We're seeing some smoke flowing in, particularly in the eastern portion of the valley," she said.

Levels of particulate suddenly spiked in Whistler Wednesday. Brent Moore of the Environmental Quality Section says very small particles are the most concerning.

"Those are the particles that are so small they're not just inhalable they're also respirable so they can go deep into the lung system," he told CTV News.

People with health issues, such as cardiovascular or respiratory issues, children and the elderly are encouraged to limit strenuous activities during periods of poor air quality.

Anyone who experiences symptoms such as chest discomfort, shortness of breath, coughing or wheezing is advised to consult their health care provider.

"This is an advisory for the general population because healthy people might even suffer some respiratory illnesses," Bates-Frymel said.

Advisories are expected to be in effect until at least Thursday afternoon.

"To clean this up we need some rain, we need some different weather systems coming in so hopefully we'll get that," she said.

With files from CTV British Columbia's Maria Weisgarber