Canada is bracing for its highest ever temperature as the country's west and swathes of the United States baked in an unprecedented heat wave, forcing schools and Covid-19 vaccination clinics to close.

The village of Lytton in British Columbia has already broken the record for Canada's all-time high, with a temperature of 46.6 degrees Celsius yesterday.

Temperatures have soared well above seasonal averages from the US state of Oregon to Canada's Arctic territories, with forecasters warning of worse to come.

"It's a desert heat - very dry and hot," David Phillips, a senior climatologist for Environment Canada, said.

"We are the second coldest country in the world and the snowiest," he said. "We often see cold snaps and blizzards but not often do we talk about hot weather like this."

"Dubai would be cooler than what we're seeing now."

Because of climate change, record-setting temperatures are becoming more frequent. Globally, the decade to 2019 was the hottest recorded, and the five hottest years have all occurred within the last five years.

Authorities have warned residents in Portland, Oregon, to stay safe in the heatwave

Yesterday in Seattle, Washington state, the temperature hit 40 degrees Celsius, a record that surprised residents not used to warmer climes.

"Normally it's probably like, maybe 60, 70 degrees (Fahrenheit) is a great day - everybody is outside in shorts and T-shirts - but this is ... ridiculous," one city resident said. "I feel like I'm in the desert or something."

Another said: "You just stand around and you're like - you can't breathe, it's so hot."

Doug Farr, manager of Seattle's weekly Ballard Farmers Market, said the site had to close early yesterday because of the heat - something it normally only has to do for snow.

"I think this is the first time we've ever closed early because of the heat," he said.

Oregon's biggest city, Portland, hit 44.4 degrees Celsius yesterday, the US National Weather Service (NWS) said, breaking the city's record set a day earlier.

In nearby Eugene, organisers were forced to postpone the final day of the US Olympic track and field trials, moving afternoon events to the evening.

Across the border in Canada, stores reportedly sold out of portable air conditioners and fans, while cities opened emergency cooling centres and outreach workers handed out bottles of water and hats as more than 160 local heat records were set, including in the ski resort town of Whistler.

Several Covid-19 vaccination clinics were cancelled and schools announced they would close due to the extreme heat.

In Vancouver, officials set up temporary water fountains and misting stations in parks and on street corners, while forest and fisheries services warned of extreme wildfire risks and low lake and river water levels stressing fish.

Environment Canada issued alerts for British Columbia, Alberta, and parts of Saskatchewan, Manitoba, Yukon and the Northwest Territories, saying the "prolonged, dangerous and historic heat wave will persist through this week."

The NWS issued a similar warning, saying the "hottest temperatures of the ongoing historic heat wave are expected across the Pacific Northwest today."

Young girls splash through a waterfall at a park in Washington DC

The scorching heat - which is breaking records in Canada and the US dating back more than 80 years - has been blamed on a high-pressure ridge trapping warm air in the region.

This heat dome poses "serious" health concerns, said Phillips, noting the last major heat in Canada left nearly 70 people dead in 2018.

"And it's not just a one-day wonder. It's a seven-day kind of thing," he said, with temperatures forecast to reach 47 degrees Celsius or higher.

"It's historically unprecedented" and "unusual because such warm temperatures typically occur in late July, early August, not June," and because of the length and the size of the heat wave.

Residents at a cooling centre in Portland

Nick Bond, an atmospheric scientist at the University of Washington, said the freak weather event was not entirely due to climate change, but was exacerbated by it.

"Climate change is a factor here, but definitely a secondary one," he said.

"The main thing going on is this highly unusual weather pattern, but that being said climate change is real, our temperatures have warmed here, especially summer night-time temperatures, and so that has just kind of raised the baseline and made this heat event that much more severe."