SUDBURY -- Environment Canada has extended a heat warning to include North Bay, Greater Sudbury, Powassan, Mattawa, West Nipissing and French River.

Those communities join previously announced warnings for Fraserdale, Pledger Lake, Kapuskasing, Hearst, Smooth Rock Falls, Fort Albany, Moosonee and Attawapiskat.

A heat event is expected through Thursday, Environment Canada said.

Daytime high temperatures will be near 30 today and in the low 30s on Wednesday and Thursday, with overnight lows near 18.

Hot and humid air can also bring deteriorating air quality and can result in the Air Quality Health Index to approach the high risk category.

"Extreme heat affects everyone," Environment Canada said in a news release. "The risks are greater for young children, pregnant women, older adults, people with chronic illnesses and people working or exercising outdoors."

Drink plenty of water even before you feel thirsty and stay in a cool place. Never leave people or pets inside a parked vehicle.

Outdoor workers should take regularly scheduled breaks in a cool place.