NEW YORK - Crowds flocked to waterfronts and swimming pools on the US East Coast and in the Midwest on Thursday to try to cope with a massive heat wave that has killed at least 22 people this week.

A boy cools off in a fountain in Brooklyn Bridge Park in Brooklyn, New York July 21, 2011. Temperatures were expected to reach near record levels Thursday as a heat wave spread east from the nation's midsection.[Photo/Agencies]

The National Weather Service issued excessive heat warnings for wide areas of the central and eastern United States, saying the combined heat and humidity could push the "real feel" temperature to 115 Fahrenheit (46 Celsius) through Saturday.

By Thursday afternoon in New York City, the thermometer hit 91F (33C) but it felt more like 112F (44C), according to AccuWeather.com.

With the promise of refreshing ocean breezes, Boston's whale-watching ships and high-speed tourist boats sold out their trips by mid-morning.

Cooling centers in Richmond, Virginia, and New York City welcomed overheated residents and a truck labeled "Water Fountain on the Go" cruised Manhattan streets, offering to refill water bottles to keep residents hydrated.

Electricity utility Con Edison said scattered outages were likely in New York in coming days with demand expected to hit all-time highs.

Unhealthy smog levels triggered by the heat were reported in Chicago, where residents were asked by the Illinois Environmental Protection Agency to reduce polluting activities such as idling vehicles and mowing lawns.

By the weekend, the heat wave is expected to cover half of the United States and affect nearly half of its 310 million people, AccuWeather.com forecaster Mary Yoon said.

"What makes this heat wave so impressive is the pure size and longevity," said Yoon.

'DANGEROUS HEALTH RISK'

Longstanding records in Philadelphia and other cities may melt away by Friday, when temperatures are expected to spike. The low pressure system that barreled east was expected to bring powerful thunderstorms with hail to northeastern states.

"Do not take this threat lightly," the National Weather Service warned on its website, noting the extreme temperatures are particularly dangerous for the elderly and the very young.

"The length of this heat wave will pose a very real and dangerous health risk to these at-risk groups and those that do not have access to air conditioning."

In the central United States, where the high temperatures have killed nearly two dozen people, more deaths were tied to the heat.

An elderly woman whose body was found in her bedroom in St. Louis, where a working air conditioner had not been turned on despite 99F (37C) temperatures, was determined on Wednesday to have died of heat stroke.

Similar causes of death were reported on Thursday in Kansas City, Missouri, where a woman in her early 80s died, and in Hutchinson, Kansas, where three elderly people were found dead in separate homes on Wednesday.

Of the people who died in Hutchinson, one had a ceiling fan and another, a 76-year-old man, had an air conditioner.

"He had an air-conditioning unit in the window but didn't use it because he didn't want to pay the electric bill," said Hutchinson Police Sergeant Thad Pickard.