LONDON, ONT. -- Environment Canada has issued a heat warning for some parts of Southwestern Ontario.

This includes WIndsor-Essex, Chatham-Kent, Sarnia-Lambton, London-Middlesex, Elgin, Oxford, Norfolk, Haldimand and Brant Counties.

A heat wave is expected to last from Thursday until Sunday, and possibly into early next week.

Daytime high temperatures in the low to mid 30s in some areas with overnight lows near 20 degrees Celsius are expected.

The humidity can also affect air quality so people with respiratory issues should beware.

"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.