Las Vegas baked on Wednesday in a record fifth consecutive day of temperatures sizzling at 115F (46.1C) or greater amid a lengthening hot spell that is expected to hit much of the US into the weekend, the National Weather Service said.

The temperature climbed to 115 at 1.13pm at Harry Reid International Airport, breaking the old mark of four consecutive days. On Sunday, the heat wave set Las Vegas’ all-time temperature record of 120F (48.8C).

Even by desert standards, the prolonged baking that Nevada’s largest city is experiencing is nearly unprecedented.

“This is the most extreme heat wave in the history of record-keeping in Las Vegas since 1937,” said meteorologist John Adair, a veteran of three decades at the National Weather Service office in southern Nevada.

Keith Bailey and Lee Doss met early on Wednesday morning at Las Vegas park to beat the heat and exercise their dogs Breakie, Ollie and Stanley.

“If I don’t get out by 8.30 in the morning, then it’s not going to happen that day,” Mr Bailey said, wearing a sunhat while the dogs played in the grass.

Alyse Sobosan said this July has been the hottest in the 15 years she has lived in Las Vegas. A counsellor at a school that is on summer break, Ms Sobosan said she does not step outside during the day if she can help it, and waits until 9pm or later to walk her dogs.

“It’s oppressively hot,” she said. “It’s like you can’t really live your life.”

It is also dangerously hot, health officials have emphasised. There have been at least nine heat-related deaths this year in Clark County, which encompasses Las Vegas, according to the county coroner’s office. But officials say the toll is likely higher.

“Even people of average age who are seemingly healthy can suffer heat illness when it’s so hot its hard for your body to cool down,” said Alexis Brignola, an epidemiologist at the Southern Nevada Health District.

The searing heat wave gripping large parts of the US also led to record daily high temperatures in Oregon, where it is suspected to have caused eight deaths, the state medical examiner’s office said.

More than 142 million people around the US were under heat alerts on Wednesday, especially in Western states.