EPA has issued poor air-quality alerts for New England, Illinois, Wisconsin and Minnesota due to smoke from fires moving south
Hundreds of wildfires are burning in Canada, from the western provinces to Nova Scotia and Quebec in the east, where there are more than 150 active fires in a particularly fierce start to the summer season.
As the country grapples with the unprecedented threat, smoke moved into parts of north-east US, where tens of millions of people were under air quality alerts on Wednesday and told to limit outdoor activity.
