It was hot enough in Toronto on Wednesday to tie — and possibly break — a decades-old daily temperature record, just hours before the arrival of summer.

CBC meteorologist Michelle Leslie said the mercury hit 34.4 C at Pearson airport in the mid-afternoon, tying a record set in 1949 and tied again in 1988. That was later revised unofficially to 34.6 C

Leslie said it wouldn’t get much cooler overnight, with the low expected to be about 25 C.

Wednesday’s hot weather also prompted GO Transit to advise commuters to expect delays during the evening rush hour as soaring temperatures cause rail tracks to swell.

When this happens, trains have to operate at reduced speeds to ensure safe travel, GO said in a note on its website.

Trains would be delayed by up to 20 minutes this evening, GO warned.

The CBC’s Jeff Semple reported that Toronto Hydro was also feeling the heat on Wednesday, as demand for power approached an all-time record for peak consumption.

Toronto Hydro warned people to conserve electricity and to expect some temporary power outages.

"It's like running your car for three, four days straight," said spokeswoman Tanya Bruckmueller. "The temperature at night's not coming down, so the cables and the equipment isn't able to cool down."

In the west end a power cable melted on Wednesday, causing a temporary power outage for several thousand customers.

'Anything that’s not snow is good for me'

CBC News spoke to a few Torontonians in the Beach who were doing outdoor activities early in the day before the temperature reached its peak.

Gillian MacKay went for an early morning run, with plans to works indoors for the rest of the day.

Gillian MacKay said that hot weather is better than the alternative. (CBC)

She said the hot weather that accompanied the last few hours of the spring was preferable to the kind of weather she dreads in the winter.

“I love it, it could be snow — and it’s not,” said MacKay. “So anything that’s not snow is good for me.”

Lynda Brown said she planned to stay indoors for the rest of the day, but she was worried about those who may not heed the warnings about the heat.

“A lot of the homeless people and the elderly, they still tend to go out and do what they have to do and I don’t think they realize how hot it really is,” she said.

The extreme alert issued by Toronto's chief medical officer of health means "in addition to using air conditioned public places such as shopping malls, local libraries and neighbourhood community centres as places to cool off, City Cooling Centres are open ... for those in need."

Environment Canada is advising the elderly and people with chronic illnesses to take it easy during the heat wave.

Dave Phillips, Environment Canada's senior climatologist, says cooler air from the north should bring some relief to southern Ontario by Friday.

With files from the CBC's Charlsie Agro