Lightning strikes the CN Tower in Toronto during a fierce thunderstorm on Aug. 24, 2011.
Environment Canada confirmed an F1 tornado southeast of Cambridge with winds between 120 km/h and 170 km/h.
The tornado touched down just after 9 p.m. at Little's Corners and tracked 15 kilometres southeast to Westover. The path of the tornado was up to 300 metres wide at times, but little damage is reported.
An agency investigator was sent to the Burlington area to check whether damage there was caused by a tornado, but that event has been classified as a downburst.
There were also reports of possible tornadoes and funnel clouds in parts of eastern Lambton County, Middlesex County, Huron-Perth and Bruce Counties.
Meanwhile, Hydro One has restored power to nearly half of the 25,000 customers throughout southern Ontario who lost their service during Wednesday night's wild weather.
About 12,000 of them had power back by late morning.
The largest outage remains near Dundas, just northwest of Hamilton, where 2,600 customers shouldn't expect to turn the lights back on until 9 p.m.