Environment Canada has issued a tornado warning for London-Middlesex and Oxford, including Woodstock and Tillsonburg.
The agency says weather radar indicates rotation in a thunderstorm to the southeast of London, near the intersection of Highway 401 and county road 74. The thunderstorm is moving to the east at 50 km/h, toward Mount Elgin.
Western Middlesex, including Strathroy and Komoka is under a severe thunderstorm warning.
Meteorologists say they are tracking a severe thunderstorm that is possibly producing a tornado. Damaging winds, large hail and locally intense rainfall are also possible.
Weather radar and a weather spotter have reported rotation in a thunderstorm near Arva, north of London. The thunderstorm is moving to the east at 50 kilometre an hour.
This is a dangerous and potentially life-threatening situation. Take cover immediately, if threatening weather approaches. If you hear a roaring sound or see a funnel cloud, swirling debris near the ground, flying debris, or any threatening weather approaching, take shelter immediately.
Go indoors to a room on the lowest floor, away from outside walls and windows, such as a basement, bathroom, stairwell or interior closet. Leave mobile homes, vehicles, tents, trailers and other temporary or free-standing shelter, and move to a strong building if you can. As a last resort, lie in a low spot and protect your head from flying debris.
Elsewhere, there are severe thunderstorm warnings in the region.
Thunderstorms are expected to develop early Saturday afternoon and last until the evening with the potential for large hail, strong wind gusts, and heavy downpours.
The agency says strong wind gusts can toss loose objects, damage weak buildings, break branches off trees and overturn large vehicles.
The Office of the Fire Marshal and Emergency Management recommends that you take cover immediately if threatening weather approaches. Lightning kills and injures Canadians every year.
