Environment Canada has issued a severe thunderstorm watch for most of eastern Ontario and parts of western Quebec, including the Ottawa-Gatineau region.

The watch was issued Sunday morning to warn that hazardous thunderstorms may develop in the afternoon and early evening. Toonie-sized hail, heavy downpours and wind gusts up to 100 km/h are possible, the weather agency wrote.

In Ontario, the watch stretches south to Cornwall and Kingston, and west to parts of Renfrew County. In Quebec, the watch includes Gatineau and communities to the northeast.

It comes as much of the region is also experiencing a lengthy heat warning which began late Friday morning.

The agency advises the public to stay indoors and take cover in a basement where possible during threatening weather, and notes strong winds can damage trees or buildings and overturn vehicles.

Environment Canada issues a severe thunderstorm watch when conditions are favourable for a storm to develop. A warning is issued when there is evidence that a thunderstorm is imminent or occurring.