Thick smoke from Canadian wildfires streams across North America skies

Millions of Americans have been urged to stay indoors and close their windows as a thick smoky haze blankets large swaths of the US. The National Weather Service has placed 12 states in the Midwest and Northeast under an orange air quality alert today, warning outdoor exercise could cause coughing, eye irritation or breathing problems. In northern Wisconsin , a red alert is also in effect, with officials urging everyone to remain indoors where and when possible. The alerts were issued after wildfire smoke blew across the border from Canada , which is experiencing its second worst fire season on record. More than 4,000 blazes have been recorded so far, with around 700 still burning.