The first weekend of fall proved to be one of the hottest of the year in southern Ontario and Quebec as heat warnings spanned the area and continue into the week.

Temperatures across the southern parts of both provinces exceeded 30 C with the humidex levels approaching the 40s over the weekend, breaking numerous heat records in the process.

Environment Canada has again issued heat warnings from Toronto to as far east as Quebec City and as north as Sault Ste. Marie, Ont., as temperatures remain in the upper 30s.

Cooler temperatures are on the horizon, however. Environment Canada forecasts a cold front coming from the west, beginning Tuesday.

While many people have been taking advantage of the summer-like temperatures, the heat and humidity pose significant safety risks -- particularly when it comes to children.

Honoré Mercier Elementary School is just one of the schools in Montreal without air conditioning, so faculty are taking extra measures to keep students safe by limiting physical activity, switching the lights off, and keeping children hydrated.

But for students attending class in school portables, the heat quickly became unbearable. This was the case at St. Cecilia Elementary School in Ottawa.

"Luckily I sat near a fan, so that kind of helped, but it was really hot," Adam Charter, a student at St. Cecilia, told CTV Ottawa.

"It was so hot you couldn't breathe," student Anthony Ianni said.

Students were eventually moved into the school's main building, which is air-conditioned.

"If the humidex gets high and we want learning to keep going, we change the conditions for students so that happens," Andrea Green, principal at St. Cecilia Elementary School, told CTV Ottawa.

Still, only about half of Ottawa's Catholic schools and 40 per cent of its public schools have full air conditioning.

In Toronto, the situation is worse. Only 125 of the Toronto District School Board's 584 schools are fully air-conditioned. But the school board says air conditioning is a matter of money.

"We're talking about hundreds of millions to install air conditioning at our remaining schools," Ryan Bird, manager of corporate and social media relations at the Toronto District School Board, told CTV Toronto. "Not to mention the electricity and operational costs for maintenance and repairs -- so, unfortunately, it's just not possible."

Ontario’s provincial government, however, says otherwise.

Mitzie Hunter, Ontario’s education minister, told CTV Toronto that $1.4 billion has been provided to boards for investment in “renewal programs.”

“School boards can choose to prioritize air conditioning and other types of repairs to schools,” Hunter said.

The Elementary Teachers Federation of Ontario is now calling on the government to set a maximum temperature for school closures, in the event of extreme heat. Meanwhile, Environment Canada is urging people to stay cool, drink plenty of water and, for those working outdoors, take regular breaks.

Over the weekend, temperatures in Montreal were at their highest since the late 1960s.

Sunday’s marathon was cancelled due to the heat. The shorter 10-kilometre and half marathon runs went on as planned, but nearly 900 people needed medical attention.

Meanwhile, temperatures in some Toronto apartments reached as high as 37 C over the weekend because landlords had to turn on the heat to comply with city bylaws that require buildings to keep a minimum temperature of 21 C between Sept. 15 and June 1.

“If by chance the reports had been wrong and on the 20th we had a frost, we could’ve been charged,” David Barkin, board president of the Avenel Non-profit Housing Corp., told CTV Toronto.

North of Toronto, residents were also enjoying the weekend heat. In Barrie, boaters took advantage of the unexpected weather and overloaded the marinas.

“It’s just been crazy,” Edward Holley of the Sturgeon Point Marina told CTV Barrie. “Everyone’s trying to get out on the water and enjoy the weather as they can.”

Cooler temperatures are on the horizon, however. Environment Canada forecasts a cold front coming from the west, beginning Tuesday.

With reports from CTV Toronto, Montreal, Ottawa, Barrie and CP24.