A punishing heat wave blanketed much of the United States Friday, leaving hot and bothered Americans flocking to swimming pools and air-conditioned malls to escape the searing temperatures.

Inside the old townhouse in northeast Washington that Ben Dooley shares with two housemates, the temperature was pushing 91 degrees Fahrenheit (33 Celsius).

That was the temperature indoors.

Outdoors in Washington, the mercury was forecast to hit 103 Fahrenheit (39 Celsius) Friday, which would equal the record for July 22.

By early afternoon, high humidity made temperatures in the US capital feel more like 116 Fahrenheit (46 Celsius) — hotter than Death Valley at daybreak.

From Texas in the southwest to Maine in the far corner of the northeast, states have been under extreme heat warnings with the record temperatures reportedly claiming 22 lives in the past week.

On Friday "bullseyes of high heat and humidity" were affecting the central states and most of the east coast, where four records were broken in the New York area, said Chris Vaccaro, a spokesman for the National Weather Service.

Newark, New Jersey, hit an all-time high temperature of 106 Fahrenheit (41 Celsius) in the early afternoon. The previous record for July 22 was 101 Fahrenheit, set in 1957.

In Manhattan's Central Park, a temperature of 102 Fahrenheit (39 Celsius) was recorded, breaking the previous record of 101 Fahrenheit set in 1957.

At John F. Kennedy International Airport in New York, the temperature reached 101 Fahrenheit, three degrees higher than the previous record set in 1998.

And Islip, Long Island, which is usually cooled by Atlantic breezes, saw temperatures Friday of 100 degrees Fahrenheit, four degrees higher than the previous record for July 22 of 96 degrees, set in 1998.

"Big cities in the east are all hitting 100," Vaccaro said. "And with there being a couple of daylight hours left, temperatures could still go up."

To beat the heat, people were streaming to swimming pools, spending long hours in air-conditioned museums or shopping malls, or sitting inside the foyers of public buildings that have opened their doors as cooling centers.

Philadelphia, the "city of brotherly love", became the city of smothering heat, with temperatures at 101 Fahrenheit by early afternoon.

Public swimming pools in the Pennsylvania city were so crowded that swimmers were asked to leave every 30 minutes to allow a new crowd to enjoy a cooling dip.

The Hidden Spring camp run by Montgomery County Parks and Recreation Service in Maryland for kids up to the age of 14, called off a much-anticipated hike to a waterfall in Thurmont, and took the 45 campers bowling instead.

"We don't have any indoor facilities, and with the heat today, it didn't seem wise to take the kids hiking. They're disappointed and so are we, but an air-conditioned bowling alley seemed a good trade-off for triple-digit heat," camp director Eric Fishman told AFP.

In New York City, the Office of Emergency Management opened cooling centers in air-conditioned public facilities for people "experiencing physical discomfort in the heat wave."

Nightfall brings little respite from the heat, with temperatures only falling to lows in the 70s or 80s Fahrenheit (20s Celsius).

"That's one of the unhealthy aspects of this heatwave: temperatures aren't retreating at night, and that taxes the body. Last night in DC, the low was 82," Vaccaro said.

Dooley described the previous night in his un-airconditioned room in northeast Washington as "unbearable" and admitted that, although not a fan of airconditioning, he was "contemplating camping in the room of my housemate who has a window air conditioner."

Another aspect of the heatwave that makes it especially dangerous is its duration — the latest surge began a week ago in the Midwest before moving eastward, and "we had another heatwave before that," Vaccaro said.

And it is also larger in scale. As many as 34 states at a time have been under heat advisories.

The high temperatures and humidity are expected to continue into the weekend until a cold front — or less-hot front — is forecast to move in.