SUDBURY -- Environment Canada has issued weather alerts for two communities in northern Ontario as the first heatwave of the season is expected Wednesday with some record-breaking temperatures.

Residents and Fort Albany and Moosonee could see temperatures reach 29 C during the day with mostly sunny skies, Canada's weather service said, and when the Humidex is factored in, it will feel more like 33 C and have a UV index of 6 or higher.

The highest temperature recorded in both Fort Albany and Moosonee for May 19 since 2010 is 20.9 C.

As of 9 a.m., the Moosonee Airport had the hottest temperature in Canada at 22.6 C, according to Environment Canada's website, at 24 C with the humidex.

"Temperatures (Wednesday night) will be unseasonably mild with an overnight low of around 18 C," said the special weather statement. "Temperatures on Thursday will start off warm but should drop sharply later in the day with the passage of a cold front."

The weather alert is issued as the "conditions pose a health risk when you are not used to the heat."

Older adults, infants, young children, and people with chronic illnesses are especially at risk from the heat.

Officials recommend staying hydrated and drinking plenty of cool liquids before feeling thirsty, dress for the weather, and spend some time in a cool place.

The temperature in Moosonee should remain above 20 C until Friday, with possible rain beginning Thursday before a drop to a single-digit high temperature on Saturday.

Parts of northwestern Ontario, near the Manitoba border to Sioux Lookout and Red Lake, are under an air quality alert due to wildfire smoke.

"Multiple wildfires continue to be observed across northwestern Ontario, with smoke resulting in poor air quality. The arrival of showers this evening may help alleviate some of the smoke concerns, but some areas may continue to see local smoke through Thursday," Environment Canada said. "If you or those in your care are exposed to wildfire smoke, consider taking extra precautions to reduce your exposure. Wildfire smoke is a constantly changing mixture of particles and gases which includes many chemicals that can be harmful to your health."

The smoke can cause throat irritation, coughing, headaches, and shortness of breath.

"If your home is not air-conditioned, be sure the house doesn't get too warm when doors and windows are closed to keep out smoke. Exposure to too much heat can also result in illness," Environment Canada said.