Canadian wildfires has crossed into the United States triggering emergency air quality alerts in over 20 states.

As reported more than 850 wildfires spread massive plume of toxic particulate matter in the atmosphere.

Prevailing northwesterly winds have funneled the dense, gray-and-yellow haze south into highly populated U.S. corridors, severely impacting major metropolitan areas.

The rapidly deteriorating conditions are driven by severe, ongoing drought and record-breaking summer heat, with major fires raging across Ontario, Quebec, Alberta, and Saskatchewan and other regions.

The air quality in large parts of the northern states of Michigan and Minnesota is deemed "hazardous" by the US Air Quality Index program, with people recommended to stay indoors.

Alerts span the Upper Midwest, the Great Lakes region and into the northeast, the US national weather service (NOAA) said in an update on........

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