Hazy air caused by central B.C.'s cluster of wildfires has spread as far west as Vancouver and as far east as Saskatchewan.

Environment Canada is now warning Canadians from the west coast to Lloyminster, Sask., about the possible health impacts of smoky air from the B.C. fires.

Until recently, Metro Vancouver had escaped the smoke from wildfires burning in the province's Interior, which have forced the evacuation of more than 45,000 people and destroyed a yet-unknown-number of homes.

Haze from wildfires in central B.C. has drifted into Metro Vancouver. (Tamara Baluja/CBC News)

That changed on Tuesday, when air quality advisories were issued for Metro Vancouver and the Fraser Valley, citing "fine particulate matter" and warning residents with respiratory problems and other medical issues to avoid strenuous activity. Infants and the elderly are particularly at risk.

The potential health impacts of poor air quality are most severe in central B.C., where wildfires have been burning out of control for more than a week.

Check out the wildfire smoke forecast for Western Canada at firesmoke.ca

Once again, Williams Lake had the poorest air quality in the province Tuesday, with the Air Quality Health Index (AQHI) hitting 23 by the late afternoon. That means anyone remaining in the evacuated city should avoid all strenuous activities outdoors.

But for those trying to stop the flames of nearby wildfires from reaching the city, that isn't possible.

A smoky haze from wildfires hangs over the Kamloops Powwow grounds where evacuee campers and RVs are parked. (Lien Yeung/CBC)

Kevin Skrepnek, fire information officer for the B.C. Wildfire Service, arrived in Williams Lake on Saturday, and said the visibility there has been poor every day.

"Our crews are out on the line, in many cases 10-12 hours a day, so we have to be managing their health," he said.

The air in Kamloops was also impacted by high levels of smoke from the wildfires, hitting an AQHI of 7. Several flights have been cancelled at the local airport over the last week because of poor visibility.

Smoke reaches the coast

A shift in the wind began sending smoke westward on Monday, according to Environment Canada meteorologist Cindy Yu.

"We are dealing with a large plume of smoke in the Interior as well as some of the nearby forest fires, and because of that we are seeing some of the smoke drifting more towards the coast under a very stable air mass," Yu said.

Smoky sunset tonight on the South Coast. <a href="https://twitter.com/hashtag/BCWildfires?src=hash">#BCWildfires</a> <a href="https://twitter.com/hashtag/Vancouver?src=hash">#Vancouver</a> <a href="https://twitter.com/hashtag/yvrwx?src=hash">#yvrwx</a> <a href="https://t.co/nWWq0DL3dQ">pic.twitter.com/nWWq0DL3dQ</a> —@JWagstaffe

It settled into valleys and along the coast overnight, meaning that many drivers had a hazy commute into Metro Vancouver.

"Unfortunately when there's fire, there will always be smoke. We'll probably have to deal with the smoky skies for another day or so," Yu said.

Wildfire smoke obscured the mountains along Howe Sound in Horseshoe Bay, just outside of Vancouver. (Deborah Goble/CBC News)

The smokiest area in the Lower Mainland is the eastern Fraser Valley, where a 188-hectare wildfire has been burning at Harrison Lake since the beginning of the month.

The AQHI there is forecast to hit 4 Tuesday, meaning there's a moderate risk to health. That means anyone with heart or breathing problems should consider reducing outdoor activities if symptoms flare up.

A change in the weather is expected to come by Wednesday night, causing the smoke to dissipate, according to Yu.

The smoky air shouldn't cause any long-term problems for healthy people, even in the heart of the wildfire zone, according to Dr. James Lu, a medical health officer with Vancouver Coastal Health.

"The issues are more for those who have chronic lung and heart disease and other chronic conditions like diabetes," he said.

"The problem with the smoke is that it could exacerbate those conditions and it's very important for them that they do have their conditions well managed as well as being able to go to places where there is cleaner air for them to breathe."