NEW YORK CITY: U.S. cities are breaking decades-old temperature records this week as a heat wave stretches from central to eastern portions of the country, the National Weather Service said on Tuesday, in what officials are warning could become a deadly weather event.

As roughly 80 million people from Indiana to New England sweltered under a heat advisory or excessive heat warning, New York Governor Kathy Hochul activated the state's Emergency Operations Center in response to high temperatures expected to last until the weekend.

"This is a deadly event," she said, one day after the city of Syracuse hit 94 degrees Fahrenheit (34.4 degrees Celsius), topping a record from 1994. "We have seen blizzards, we have seen flooding, we had hurricanes, we had tornadoes. But this heat event is most likely to cause more deaths."

New York state will open its beaches and public pools early, in time for people to enjoy them over the Juneteenth holiday on Wednesday. Under its heat emergency plan, New York City is opening its cooling centers for the first time this year.

Chicago registered 97 degrees F at Chicago O'Hare International Airport on Monday, which broke a record of 96 degrees F set in 1957. Temperatures hovered around 91 degrees F on Tuesday, with the heat index, which factors in temperature and humidity to measure how hot it feels, touching 95 degrees F.

To cool off, Breanne Trammell, 43, and her poodle-mix dog Moe were planning to hit Montrose Dog Beach on Chicago's Lake Michigan.

But with one stop first.

"We're out at the store getting an air conditioner," she told Reuters by telephone. She's spending all her birthday money - US$400 from her mother - for a new unit.

"You don't know how hot my apartment is," said Trammell, who turned 44 on Wednesday. "It's dreadful, for me and Moe. You feel heavy even breathing. It's oppressive. Miserable."

She and her friends have been going to movies and bowling alleys, anywhere to keep cool lately, but it's overwhelming when it doesn't cool off at night, she said.

Teams of city workers scattered across Chicago to homeless camps, trying to coax people to escape the heat in shelters, said Brian Berg, a spokesperson for the city's Department of Family Services and Support.

"We check all the sites," Berg said. "We provide them with not only water and food, but we'll take them to the shelters, which are also cooling stations."

High temperatures can cause dehydration, heat exhaustion and heatstroke, and worsen pre-existing conditions like cardiovascular problems.

Detroit and Philadelphia, as well as cities in New Hampshire, Connecticut and Maine are also due for record temperatures in the coming days, NWS meteorologist Marc Chenard said.

Out west, firefighters battled high temperatures, low humidity and strong winds as they sought to contain a wildfire that started Saturday northwest of Los Angeles and has burned 12,000 acres. The blaze forced about 1,200 people to evacuate the Hungry Valley outdoor recreation area.

In southern New Mexico, wildfires burned to the north and south of Ruidoso village, forcing the community of around 8,000 people to evacuate, local authorities said on Tuesday.

While it is too soon to say if the heat is driven by climate change, this heat wave is occurring earlier in the year than the historical average. Central Maine is running 30 degrees above average, he added.

"It's kind of early in the season to be getting this long of a duration of heat wave for the Ohio Valley and New England," Chenard said, adding that it was dangerous because people were not prepared.

 - Reuters