Originally Published: 30 JUN 21 07:58 ET

Updated: 30 JUN 21 14:21 ET

By Aya Elamroussi, CNN

(CNN) -- The extreme heat wave in the Northwest is beginning to subside in Seattle and Portland, Oregon, but much of the West will continue to deal with baking temperatures as millions remain under heat alerts.

Canada and US cities in the Northwest have reported their hottest temperatures on record. More than 52 million people are under a heat warning or advisory from coast to coast.

Three potential deaths associated with heat-related illness were reported Sunday and Monday, according to Washington Department of Health spokesman Cory Portner.

While temperatures are likely to let up in the Northeast by Wednesday's end, the heat is expected to last in the Northwest well into mid-July, CNN's meteorologist Michael Guy predicted.

"The Northeast will continue to be hot (Wednesday), before a cold front drops temperatures, but also brings the risk for severe storms this afternoon and evening," Guy said.

Portland set an all-time, record-high temperature three days in a row, topping out at 116 degrees on Monday. Seattle hit 108 degrees, breaking the all-time record it set just a day earlier.

Across the border, Lytton, British Columbia, hit 121 degrees on Tuesday -- the highest temperature ever recorded in Canada. The record was broken on Sunday and then again on Monday.

Kristina Dahl, a senior climate scientist at the Union of Concerned Scientists, says the heat wave is "unprecedented."

"We saw heat records over the weekend only to be broken again the next day," Dahl told CNN, "particularly for a part of the country where this type of heat does not happen very often."

Multiple experts, including Pennsylvania State University's climate scientist Michael E. Mann, have blamed one thing for the soaring temperatures -- climate change.

"You warm up the planet, you're going to see an increased incidence of heat extremes," Mann told CNN.

Heat blamed for dozens of deaths and even more emergency room visits

At least 676 people in Washington state visited emergency departments for heat-related symptoms from Friday through Sunday -- before the heat wave hit its peak.

On Monday alone, there were 688 heat-related emergency department visits, according to Portner, who said the state had recorded at least 1,384 hospital visits related to the heat since the weekend.

In addition to the three potential deaths connected to heat-related illnesses, Portner said officials were looking into one potential death associated with submersion and drowning.

King County, which is home to Seattle, had 40 emergency department visits for heat-related illness on Saturday and 91 on Sunday, according to Gabriel Spitzer, communications specialist for Public Health Seattle & King County.

On Monday, there were 223 emergency department visits for heat-related illness among King County residents, according to Spitzer.

The eastern Washington city of Spokane hit 109 degrees, breaking the previous record of 108 degrees set on August 4, 1961, according to National Weather Service Spokane.

The city of Wenatchee, Washington, broke an all-time heat record, reaching 114 degrees. And Omak, Washington, hit 117 degrees, shattering the previous record of 114 degrees set on July 4, 1928.

Volunteers with the United Farm Workers in Prosser, Washington, distributed water and Gatorade in the cherry fields, according to the UFW Facebook page.

The high in Prosser reached 113 degrees on Tuesday.

In Oregon, a total of 506 heat-related visits to emergency departments and urgent care centers were reported by the state's health authority. At least 251 visits occurred on Monday alone, when temperatures were highest.

In the Portland area, the 97 emergency department and urgent care clinic visits for heat illness is nearly the same number of cases they would expect to see all summer, according to Multnomah County communications director Julie Sullivan-Springhetti.

"The record breaking heat also broke records for calls for help. Emergency calls, visits to the emergency rooms, and calls for people and pets reached all-time highs," Sullivan-Springhetti said in an email to CNN.

Along the West Coast, more than 20 million people were under a heat warning or advisory, from the Canadian border to the Mexican border.

Meanwhile, more than 230 deaths have been reported in British Columbia since Friday as a historic heat wave brought record-high temperatures there, officials said Tuesday.

"Since the onset of the heat wave late last week, the BC Coroners Service has experienced a significant increase in deaths reported where it is suspected that extreme heat has been contributory," Chief Coroner Lisa Lapointe said in a statement.

In Vancouver, officers have responded to more than 65 sudden deaths since the heat wave began on Friday, prompting the Royal Canadian Mounted Police to issue a statement about a "concerning increase in sudden deaths amid the heat wave."

Royal Canadian Mounted Police responded to 35 sudden deaths in Surrey, British Columbia, since Monday, media relations officer Cst. Sarbjit K. Sangha told CNN.

"While the causes of death has not yet been determined in each of these cases, we can confirm that Surrey RCMP is responding to a higher than usual number of deaths since the beginning of the extreme weather conditions," Sangha said.

In the nearby city of Burnaby, police responded to more than 25 sudden death calls in a 24-hour period since Monday, with heat believed to be a contributing factor in the majority of the deaths, according to a release from RCMP.

"We are seeing this weather can be deadly for vulnerable members of our community, especially the elderly and those with underlying health issues. It is imperative we check on one another during this extreme heat," Cpl. Mike Kalanj with Burnaby RCMP said.