Toronto residents are waking up to smoky skies after wildfire smoke drifting from northwestern Ontario triggered an air quality warning across the city.

Environment Canada has issued an orange air quality alert, warning that smoke could linger through Thursday and urging people to limit time outdoors, especially for sports, exercise and other strenuous activities.

The situation became even more concerning Wednesday morning when IQAir ranked Toronto as having the worst air quality in the world, with thick smoke reducing visibility across the city.

The smoke may cause eye, nose and throat irritation, headaches and coughing, while those with asthma, heart or lung conditions, seniors, pregnant people and young children are at greater risk of more serious health effects.

Officials recommend keeping windows and doors closed as much as possible and using air conditioning or air filtration if available.

Adding to the challenge, Toronto remains under a heat warning, with temperatures expected to reach 33°C, feeling closer to 36°C with the humidity. Environment Canada says the combination of extreme heat and poor air quality can increase health risks, encouraging residents to stay hydrated, reduce outdoor activity and watch for signs of heat exhaustion.