Environment Canada issued a severe thunderstorm warning for a large part of central and southwestern Ontario Tuesday afternoon.
The warning is in effect for communities in the Simcoe County region, Newmarket, and those north of Kitchener and Guelph, reaching up to Lake Huron and Georgian Bay.
The national weather agency warns several areas are experiencing dangerous thunderstorms.
If it progresses, Environment Canada predicts wind gusts may reach up to 90 km/h and hail the size of a toonie could form.
The storm is expected to develop Tuesday afternoon into the evening.
The weather agency cautions that the large hail may damage property, break windows, dent vehicles and cause serious injury.
The strong winds also have the potential to toss loose objects, damage weak buildings, break branches off trees and overturn large vehicles.
Heavy rain and lightning are also possible, the weather agency warns.
Emergency Management Ontario recommends that residents take cover immediately if threatening weather approaches.
Severe thunderstorm watches are issued when atmospheric conditions are favourable for developing thunderstorms that could produce large hail, damaging winds, or torrential rainfall.