City officials have issued the first extreme heat alert of the season as soaring temperatures smash weather records across the province.

Toronto hit a record high of 31 C, breaking a record of 30.6 C set in 1944, said Dave Phillips, a senior climatologist with Environment Canada.

It was the second record day in a row. Experts say its going to be a long, hot summer.

On Tuesday, city dwellers experienced a high of 28.8 C, almost a full degree warmer than a 2007 record of 28.1 C, he said.

Record highs have also been recorded in Peterborough, Ottawa, North Bay and Sudbury.

The blast of heat, which arrived last week from the Ohio Valley region, prompted Toronto Public Health to open seven cooling centres across Toronto.

Warmer than normal temperatures are expected to keep Ontario as well as parts of Quebec warm through the end of May.

"This [weather] seems to be coming more from the south western part of the United States…avoiding the industrial heartland. So, it arrives as cleaner air, but it's still pretty moist and obviously quite warm," Phillips said.

Environment Canada warned of torrential rain, hail and possible tornadoes near Timmins and in the Kirkland Lake region Wednesday afternoon.

Phillips is anticipating a warmer than usual summer from coast to coast.

"What you see is what you're going to get," he said.

"It's likely to be, our models are showing, warmer than normal. You can never tell with precipitation, it's always a tough call, but we've had the warmest winter on record, the warmest spring on record and now it looks like it's non-stop.

"Last summer, I think it was characterized by maybe not enough summer, this summer it might be too much summer."