A brutal heat wave has gripped the eastern part of the United States as tens of millions of people sweltered in record high temperatures on Tuesday.

A climate phenomenon called a "heat dome" has sent temperatures soaring to dangerous triple digits in some cities while also trigerring extreme humidity.

A heat dome occurs when high pressure in the upper atmosphere traps heat and humidity, increasing temperatures in the lower atmosphere.

New York bears the brunt

New York City's John F. Kennedy Airport reported a temperature of 100 degrees Fahrenheit (38 Celsius) shortly after noon — the first time since 2013.

Temperatures in Central Park were forecasted to reach 99 F (37 Celsius), beating the area's previous high of 96.

Cities like Boston and Batlimore also saw temperatures rising to 101 degrees Fahrenheit. 

"It looks like today is probably the worst day for widespread heat records," news agency Reuters quoted Bob Oravec, lead forecaster at the National Weather Service in College Park, Maryland, as saying.

Millions battle the heat

Hospitals in some places saw people arriving with heat-related illnesses.

The scorching heat also caused disruptions to public transport, including delays of Amtrak trains.

As over 150 million people received heat warnings, utilities called on customers to conserve power.

Meanwhile, electronics stores in the region reported a huge spike in the sale of air conditioners and fans.

The National Weather Service said that the heat would not subside entirely by the weekend but swathes of the eastern US could see improved conditions in the next few days.

Edited by: Roshni Majumdar