Officials in Montreal and the Eastern Townships are urging people to check on their neighbours and loved ones, especially those without access to air conditioning, as the heat wave gripping the regions peaks and is being blamed for 18 deaths.

The toll of heat-related deaths in the province rose by eight in total between Tuesday and Wednesday. Twelve have been confirmed in the Montreal area, five in the Eastern Townships and one in Laval.

The wave started last Friday and is the worst to hit Quebec in decades.

Mayor asks for public's help

Montreal Mayor Valérie Plante said at a news conference that, "we're doing everything we can." She pointed to the city's response, which includes opening swimming pools and air-conditioned areas to the public, distributing water to those in need and having first responders checking in on vulnerable citizens.

Plante said 15,000 people were visited by firefighters and police yesterday to make sure they could cope with the heat.

She also called on the public for help responding to the heatwave.

"I'm counting on Montrealers to knock on doors, maybe of a neighbour, just to find out if the person is OK. It's a team effort," Plante said.

Check on the elderly

"Think about your neighbours; think about your family members, grandpa, grandma; think about your kids, your friends," said Mélissa Généreux, the director of public health in the Eastern Townships.

"Why not give them a call, a visit, take them out of the house … a bit of cool air could do some good and save lives."

Généreux and David Kaiser, of Montreal's public health department, have said those who died in both regions didn't have air conditioning in their homes and had health issues.

Environment Canada issued a heat warning for the Montreal region Wednesday. (Radio-Canada)

Speaking on CBC's The Current, Kaiser said temperatures recorded by paramedics in these cases reached the high 30s inside the victims' apartments.

"What we know about why heat kills people is that people with underlying medical problems are more vulnerable to accumulating heat," Kaiser said.

"So, after a couple days of being hot and living in a place with no air conditioning, the heat just overwhelms the body's capacity to adapt."

Kaiser said city workers are knocking on doors to identify people in similar situations and get them medical help, or to a cooling shelter.

My thoughts are with the loved ones of those who have died in Quebec during this heat wave. The record temperatures are expected to continue in central & eastern Canada, so make sure you know how to protect yourself & your family: <a href="https://t.co/JSPPsU80x9">https://t.co/JSPPsU80x9</a> —@JustinTrudeau

The hot and humid air mass over southern Quebec will persist through Thursday, but lift by Friday, when a cooler 24 C is expected to settle in, according to Environment Canada.

"Humidex values will reach near 40," states Environment Canada's heat warning for the Greater Montreal area. "However, conditions will grow even more uncomfortable on Thursday with humidex values reaching 43."

Today, temperatures are expected to reach a high of 34 C with a very high UV index. Thursday should be more of the same.

Urgences-Santé flooded with calls

Urgences-Santé said it had received more than 1,200 calls a day since the heat began, representing a 30 per cent increase to its busiest days.

The ambulance service urges people to first seek help from friends and family or to call 811 first for tips on how to handle minor health issues where life is not at risk.

Urgences-Santé is asking people to avoid calling 911 for heat-related illnesses and instead seek help from friends, family or 811 as mild symptoms can be easily remedied without medical intervention. (Radio-Canada)

The paramedic service's president, Nicola D'Ulisse, said Urgences-Santé has reached the "limit of the capabilities of our services and we now need the collaboration of our citizens to provide quality service to all.

The city has taken a number of measures, including extending pool hours to help people cope with the heat.

Généreux said health workers have not been spared, with several suffering from heat exhaustion.

Symptoms to watch out for include dizziness, fainting and confusion, she said.

Many of those who've called 811 in the Eastern Townships have been related to cases involving children, Généreux said. She invited older people to use the service, stressing their vulnerability to the heat.