Temperatures are soaring across Ontario, as well as parts of southern Quebec, prompting Environment Canada to issue heat warnings throughout the regions.

Toronto is experiencing the hottest day of the year so far, with temperatures predicted to reach 34 C on Wednesday afternoon. It will feel closer to 40 C with the humidex.

Wednesday marked the third day in a row that Toronto experienced searing temperatures and high humidity, prompting the city to issue an extreme heat alert.

Environment Canada has also issued heat warnings on Wednesday for Metro Montreal, areas of northern Ontario, including Sudbury and North Bay, and for the Ottawa-Gatineau region, where temperatures were expected to break records on Wednesday.

While the heat warning is in effect, Environment Canada is advising residents to try to stay cool, drink lots of water, and be on the lookout for symptoms of heat illness.

Elderly people, children, and those with chronic illness are at increased risk of developing heat stroke or heat exhaustion, and the agency urges friends, family, and neighbours to check in on the vulnerable and monitor for signs of illness.

Symptoms of heat related illness include:

  • dizziness or fainting, nausea or vomiting
  • headache
  • rapid breathing and heartbeat
  • extreme thirst and
  • decreased urination with unusually dark yellow urine

If somebody is experiencing these symptoms, Environment Canada recommends that person get to a cool space and drink lots of liquids, preferably water.

To keep cool, Environment Canada recommends wearing light-coloured, loose clothing and wide-brimmed hats, and keeping blinds or drapes closed if air conditioning isn't an option.

It also recommends seeking cool, air conditioned public spaces, such as shopping malls, libraries, and community centres.

"People have to stay cool as much as possible. Avoid going out in the heat or being physically active in the heat," Anthony Levinson, a psychiatry and neuroscience professor at McMaster University, told CTV News Channel.

On its website, Environment Canada said some areas may see relief from the heat as early as Thursday, but that high temperatures in the Greater Toronto Area are expected to last until the weekend.

The following areas fall under Environment Canada's heat warning.

Southern Ontario

  • Belleville - Quinte - Northumberland
  • Brockville - Leeds and Grenville
  • City of Hamilton
  • City of Ottawa
  • City of Toronto
  • Cornwall - Morrisburg
  • Halton - Peel
  • Kingston - Prince Edward
  • Niagara
  • Prescott and Russell
  • Smiths Falls - Lanark - Sharbot Lake
  • Stirling - Tweed - South Frontenac
  • York - Durham

Northern Ontario:

  • Attawapiskat
  • Chapleau - Gogama
  • Elliot Lake - Ranger Lake
  • Greater Sudbury and vicinity
  • Kapuskasing - Hearst
  • Kirkland Lake - New Liskeard - Temagami
  • Manitoulin - Blind River - Killarney
  • Moosonee - Fort Albany
  • North Bay - West Nipissing
  • Timmins - Cochrane

Southern Quebec

  • Gatineau
  • Lachute - Saint-Jerome
  • Lanaudiere
  • Laurentians
  • Metro Montreal - Laval
  • Richelieu Valley - Saint-Hyacinthe
  • Upper Gatineau - Lievre - Papineau
  • Vaudreuil - Soulanges - Huntingdon