A teenage girl is recovering from a lightning strike after the tent she was in was hit during Saturday's violent thunderstorm.

The girl had been attending the Wakestock festival on the Toronto islands. She had taken shelter from the storm with three others when the tent they were in was struck. The girl did not lose consciousness and is reportedly uninjured.

Severe thunder and hailstorms hit a wide swath of southern Ontario, prompting Environment Canada to warn residents to stay inside.

"This is a warning that severe thunderstorms are imminent," an alert issued by the agency said. "Emergency Management Ontario recommends taking cover immediately when threatening weather approaches."

Areas such as Toronto, Hamilton, Vaughan, Guelph, Lindsay, St. Catharines, London and Kitchener were included in the severe storm warning.

The storms began forming in a line between Lake Simcoe, King City, and London shortly after 1 p.m. They were clocked at 50 kilometres per hour and were travelling eastward.

"These storms will be severe with large hail up to four centimetres (in) diameter," said Environment Canada, predicting "damaging" winds up to 90 kilometres per hour as well as "torrential downpours" of 50 millimetres of rain per hour.

Late in the afternoon, residents east of Toronto were still experiencing the harsh conditions.

The weather put a damper on numerous outdoor events being held in the city on Saturday, including a rally in support of Guantanamo Bay detainee Omar Khadr, the Beaches Jazz Festival, the Just for Laughs festival on Yonge Street and Jamaica Day in Keelesdale Park on Eglinton Avenue West.