Canadian wildfires are sending smoke billowing — and plunging air quality — across the US this week

• Get ready for more hazy days in the US this week as Canadian wildfires send smoke south again.
• On Tuesday, maps and pictures showed extreme haze in Chicago.

Canadian wildfires are sending smoke back across the US this week, plunging the air quality in major cities and prompting health advisories.

On Tuesday, Chicago was blanketed with thick haze from the wildfires and at one point had one of the worst air qualities in the world, according to AirNow and air quality indexes.

City officials put the city and surrounding areas under air quality advisories.

Milwaukee and Detroit also saw harmful air quality from the wildfire smoke, according to CBS News.

Photos posted on Twitter also showed the hazy conditions.

The smoke is also expected to return to New York City tomorrow and Thursday, Governor Kathy Hochul announced on Tuesday.

"Air quality is expected to reach unhealthy levels in some areas," Hochul tweeted, adding that air quality health advisories had been issued in some areas.

The Canadian wildfire smoke previously plagued areas of the northeastern US earlier this month, covering major cities such as New York City in an orange hazy smoke.