Environment Canada has issued tornado warnings for parts of cottage country, including Parry Sound, Muskoka and Barrie.
The tornado warnings issued around 3 p.m. on Friday also applied to Orillia, Midland and Grey and Bruce counties.
Earlier in the day, the federal weather agency issued a severe thunderstorm watch for Toronto and parts of the GTA.
York, Peel, Durham and Halton regions were also affected.
CityNews meteorologist Adam Stiles warned that a series of storm systems, with the potential for strong winds and downpours, were on their way to the GTA.
“There’s a potential for thunderstorm activity toward the overnight,” and the chance of rain earlier in the day, he said.
“From the late evening to about two o’clock in the morning is our greatest risk. We could see some pop up showers before that,” he said.
Click here for the full weather forecast.
Toronto is also under an extreme heat alert for the fourth day, with a high of 34 C in the forecast.
“It will be warm and muggy into Saturday morning but will be fresher on Saturday afternoon,” Stiles said.
During an extreme heat alert, Toronto officials are asking people to check on those who may be vulnerable to the heat, especially isolated adults, seniors and the chronically ill.
The city has opened cooling centres and extended hours at public pools to help residents cope.
Click here for a full list of cooling centre locations.
Click here for extended public pool hours.