A sweltering heatwave that has settled over western Canada for several days is believed to be a contributing factor in dozens of sudden-death calls received by police in the Vancouver area, authorities have said.

Cpl Mike Kalanj, of Burnaby Royal Canadian Mounted Police, said the detachment responded to 25 sudden-death calls in a 24-hour period. The deaths are still under investigation and many of the deceased were elderly, he said.

Temperatures in the Vancouver area reached just under 32C (90F) on Monday, but the humidity made it feel close to 40C (104F) in areas that are not near water, Environment Canada said.

The record-breaking heatwave could ease over parts of British Columbia, Yukon and the Northwest Territories by Wednesday, but any reprieve for the Prairie provinces is further off.

In Vancouver, the police department said it had redeployed dozens of officers and asked the public to call 911 only for emergencies because heat-related deaths had depleted frontline resources and delayed response times.

"Vancouver has never experienced heat like this, and sadly dozens of people are dying because of it," said Sgt Steve Addison. "Our officers are stretched thin, but we're still doing everything we can to keep people safe."

As of mid-afternoon on Tuesday, he said, police had responded to more than 65 sudden deaths since the heatwave began on Friday.

"The vast majority of these cases are related to the heat," he said, adding that on a typical day, Vancouver police respond to between three and four sudden-death calls.

Ingrid Jarrett, CEO of the British Columbia Hotel Association, said residents in parts of the Lower Mainland, Victoria and the Okanagan region have been booking air-conditioned rooms so they can continue working and also get some sleep.

Environment Canada said the weather system shattered 103 heat records across British Columbia, Alberta, Yukon and the Northwest Territories on Monday.

Those records include a new Canadian high temperature of 47.9C (118F) set in Lytton, British Columbia, smashing the previous record of 46.6C (116F) set in the same village a day earlier.

In the Northwest US, the heatwave moved inland on Tuesday, prompting an electrical utility in Spokane, Washington, to resume rolling blackouts amid heavy power demand.

Officials said more than a half-dozen deaths in Washington and Oregon may be tied to the intense heat that began late last week.

The dangerous weather that gave Seattle and Portland consecutive days of record high temperatures exceeding 100 degrees Fahrenheit (37.7 degrees Celcius) was expected to ease in those cities. But inland Spokane saw temperatures spike.

The National Weather Service said the mercury reached 109 F (42.2 C) in Spokane - the highest temperature ever recorded there.

About 9,300 Avista Utilities customers in Spokane lost power on Monday and the company said more planned blackouts began on Tuesday afternoon in the city of about 220,000 people.

Heather Rosentrater, an Avista vice president for energy delivery, said: "We try to limit outages to one hour per customer."

She said about 2,400 customers were without power as of shortly after 2pm on Tuesday, mostly on the north side of the city, and those customers had been alerted about the planned outage.

About 21,000 customers were warned on Tuesday morning that they might experience an outage, she said.

Avista had to implement deliberate blackouts on Monday because "the electric system experienced a new peak demand, and the strain of the high temperatures impacted the system in a way that required us to proactively turn off power for some customers", said company president and chief executive Dennis Vermillion.

"This happened faster than anticipated."

Ms Rosentrater said the outages were a distribution problem, and did not stem from a lack of electricity in the system.

Meanwhile, authorities said multiple recent deaths in the region were possibly related to the scorching weather.

The heat may have claimed the life of a worker on a nursery in Oregon, the state's worker safety agency, known as Oregon OSHA, said on Tuesday.

The man who died was from Guatemala and had apparently arrived in the US only a few months ago, said Andres Pablo Lucas, owner of Brother Farm Labour Contractor that provided workers for the nursery, including the man who died.

Agency spokesman Aaron Corvin said: "The employee was working on a crew moving irrigation lines. At the end of the shift he was found unresponsive in the field."

Officials in Bremerton, Washington, said heat may have contributed to four deaths in that Puget Sound city.

But Vince Hlavaty, Bremerton's medical officer, told the Kitsap Sun that firefighters cannot say definitively whether the heat was the cause of death.

In Bend, Oregon, authorities said the deaths of two homeless people in extreme heat may have been weather-related.

The United Farm Workers (UFW) urged Washington governor Jay Inslee to immediately issue emergency heat standards protecting all farm and other outdoor workers in the state with a strong agricultural sector.

The state's current heat standards fall short of safeguards the UFW first won in California in 2005 that have prevented deaths and illnesses from heat stroke, the union said in a statement.

Unlike workers in California, Washington state farm workers do not have the right to work shade and breaks amid extreme temperatures.

The heatwave was caused by what meteorologists described as a dome of high pressure over the Northwest and worsened by human-caused climate change, which is making such extreme weather events more likely and more extreme.