Canada wildfire smoke leaves millions under air quality advisory

Wildfires, like this one in British Columbia's Tweedsmuir Provincial Park, continue to burn in Canada.

Smoke from Canada's wildfires has again blanketed swathes of the US, leaving tens of millions of Americans under air quality advisories.

Several states along the east coast had air quality ratings on Tuesday in the 150s, considered "unhealthy" by the US government.

Air quality conditions in parts of North America have experienced historic lows since June.

Canada has seen its worst wildfire season on record this summer.

Health officials have warned of medium to high smoke risk in cities across Canada, including Calgary, Montreal, Quebec and Toronto.

US regions with an AQI over 150 on Tuesday afternoon included parts of Georgia, Tennessee, North Carolina, South Carolina, Vermont and New Hampshire, according to AirNow, which tracks airborne pollutants.

The smoke is forecast to begin dissipating on the US east coast by Wednesday.

• Is climate change fuelling Canada's wildfires?

• Canada wildfire crews try to control the uncontrollable

Nearly 900 fires are burning across Canada, with 590 out of control, according to the Canadian Interagency Forest Fire Centre.

Two firefighters have died in the past week tackling the blazes - one in the Northwest Territories and a 19-year-old in southern British Columbia.

On Monday, health officials in British Columbia said the death of a nine-year-old boy with asthma may also be linked to wildfire smoke.

"The sudden and unexpected death of this young boy is a heart-breaking loss for his family and community," said the BC Coroners Service, which is investigating the child's death.

Wildfires have razed over 24 million acres (10 million hectares) in Canada so far this year - an area roughly the size of Iceland or the US state of Indiana.

Climate change increases the risk of the hot, dry weather that is likely to fuel wildfires.

The world has already warmed by about 1.1C since the industrial era began and temperatures will keep rising unless governments around the world make steep cuts to emissions.