Smoke has drifted into southern British Columbia from raging wildfires in Washington state, as Canadian crews get ready to offer relief to exhausted U.S. firefighters.

Metro Vancouver has issued an air quality advisory for the central and eastern Fraser Valley because of elevated concentrations of fine particulate matter.

"People with chronic underlying medical conditions should postpone strenuous exercise until the advisory is lifted," said Metro Vancouver in a statement. "Staying indoors and in air conditioned spaces helps to reduce fine particulate exposure."

Exposure to the fine particulates in smoke is a concern for infants, the elderly and those who have diabetes, lung or heart disease.

CBC reporter Brady Strachan tweeted this shot of the sun in Kelowna Sunday morning. (Brady Strachan/CBC)

The BC Wildfire Service says the smoke arrived in B.C. Saturday night due to strong southerly winds where it was trapped in the valley bottoms by a temperature inversion.

The most active fire in the Kamloops Fire Centre is the 3,100 hectare Testalinden Creek wildfire south of Oliver. Firefighters are reassessing their tactics today because reduced visibility due to smoke could hamper the aerial attack on that fire.

The fire centre also warns that new wildfires will be difficult to spot in the haze and is asking the public to be vigilant and report new fires. It says forecasts indicate the wildfire smoke is expected to remain for the next few days.

Meanwhile, the B.C. Wildfire Service is sending 33 of its firefighters to help U.S. crews fight the Stickpin wildfire in Washington State burning just 4.5 kilometres south of the Canadian border.

The 192-square kilometre fire has grown toward the east, but has not grown closer to the border over the weekend.