NEW YORK - US cities opened special "cooling centers" amid a national heat wave that ramped up energy demand and caused a lengthy outage at one of the country's busiest airports.

Temperatures in many regions soared into triple digits, breaking records and leaving resident cradling their air conditioners for comfort.

For New Yorkers, the Big Apple was more like the Baked Apple, and transport woes did nothing to soothe people's frazzled nerves.

At the city's LaGuardia international airport, one of the main terminals had to be shut down after the power went out at 8:00 am (1200 GMT), leaving hundreds of passengers stranded.

The electricity utility Con Edison said the spike in commercial and domestic power demand had caused problems with the main feeder cables servicing the airport.

Monday saw the mercury hit 98 degrees Fahrenheit (37 degrees Celsius) at LaGuardia -- the highest temperature registered since records started being kept in 1948.

Six hours after the outage began, Con Edison teams were still struggling to restore power.

The terminal closure affected American Airlines and Delta Shuttle flights.

"It hasn't been a madhouse. It's been largely manageable," said Port Authority spokesman Pasquale DiFulco. "That said, we'll be happy when everything's back up and running."

One of New York's main subway lines servicing western Manhattan also lost power Tuesday, grinding to a halt for one and a half hours shortly after the morning rush hour.

"We're not sure if the heat was to blame, but it certainly didn't help," said one New York City Transit official.

The municipal authorities ordered the opening of so-called cooling centers across the city -- air-conditioned facilities normally located in senior citizen and community centers, for use by the general public.

The four-day heat wave, caused by a high-pressure system to the south pumping in hot air from Mexico, resulted in heat advisories being posted in the South, Midwest and Northeast United States.

Record temperatures were also set in Stockton, California (110 degrees) and Salt Lake City, Utah (103 degrees).

"A heatwave like this usually comes about once a year," said a spokesman for the National Weather Service. "The important thing is for people to exercise some common sense, drink enough water and wear light clothes."

A cold front moving in from the Northwest was expected to bring some relief to the country on Wednesday.