A severe storm system tracking across southern Ontario has prompted Environment Canada to issue tornado warnings for a large part of the region.

The agency's meteorologists say a swirling band of thunderstorms and heavy rain is sweeping eastward, bringing a risk of tornadoes to a number of places including Kitchener, Waterloo, Cambridge, Burlington, Oakville, Milton, Erin, and southern Wellington county.

Severe thunderstorm watches are in place in much of the region, including Toronto.

Senior meteorologist Geoff Coulson is advising people to brace for an afternoon of heavy downpours, high winds and possibly twisters.

A hot, humid and unstable air mass over southern Ontario has already sparked severe thunderstorms, which are moving quickly.

Additional storm activity is expected to develop later in the day.