Firefighters in Canada are battling more than 50 forest fires that have sparked smog alerts across Quebec and parts of the north-eastern US.
At least eight of the blazes north of Montreal were out of control, Quebec's forest fire protection unit said.
Smoke moved over Massachusetts and New Hampshire in the US, with the city of Boston covered in a haze on Monday.
Officials in both countries have warned people with breathing problems to remain indoors until the smoke clears.
The fires - sparked by lightning strikes - have raged for a week, and more than 1,300 firefighters were battling the blazes on Monday evening.
More than 1,260 sq km of Quebec forest have been scorched, according to the provincial forest fire protection authority.
One of the hardest hit areas has been Wemotaci, a native reserve in Central Quebec that is home to Atikamekw indigenous group.
Unseasonably warm and dry weather conditions have made Quebec's spring fire season particularly active in 2010, reports say.