Residents across the Greater Toronto Area woke to orange-tinted skies Wednesday as smoke from forest fires in northwestern Ontario settled over the region, dropping Toronto's air quality to among the worst in the world.

According to Global News, IQAir — a Swiss air quality technology company that runs the world's largest real-time air quality platform — ranked Toronto as the worst major city for air quality for most of Wednesday morning and early afternoon, ahead of Kinshasa, Delhi, Dubai and Jerusalem.

Environment Canada issued an orange air quality warning covering much of southern Ontario, saying the smoke could persist into Friday for some areas. The agency advised people to limit time outdoors and stay cool inside.

"Seek immediate medical assistance" if symptoms are serious

"You may experience mild and common symptoms such as eye, nose and throat irritation, headaches or a mild cough. More serious but less common symptoms include wheezing, chest pains or severe cough. If you think you are having a medical emergency, seek immediate medical assistance." — Environment Canada

The agency said people at higher risk from wildfire smoke — including those aged 65 and older, pregnant people, infants and young children, people with existing illnesses or chronic health conditions, and outdoor workers — should avoid strenuous activity outside and seek medical attention if symptoms develop.

Heat warning still in effect

The poor air quality comes on top of a heat warning that has been in place since Monday. Environment Canada said maximum temperatures of 30 to 36 C are expected Wednesday, with humidex values making it feel like 38 to 42 C.

The heat is expected to continue into the evening and could carry into Thursday or Friday in areas near Lake Erie and Lake Ontario. Tuesday was the most intense day of the heat wave so far, with humidex values making it feel like 38 to 45 C in parts of southern Ontario.

FIFA Fan Festival cancelled

The orange skies have already forced at least one major event off the schedule. FIFA Fan Festival, which has been hosting World Cup watch parties in Toronto, cancelled Wednesday's event because of the air quality warning.

Organizers said in a statement that the health and safety of attendees, staff, volunteers and emergency personnel remains their top priority, and that premium ticket holders will be contacted directly about refunds.

For GTA residents, the combined warnings mean a day of keeping windows closed, running air conditioning where possible, and checking on older neighbours and anyone with breathing conditions. Environment Canada's air quality statement remains in effect, and anyone experiencing severe symptoms is being told to seek immediate medical help.