A wave of intense heat disrupted Fourth of July celebrations across large parts of the central and eastern United States on Friday, forcing officials to cancel or postpone dozens of parades, concerts and fireworks displays as the country marks 250 years since its founding, according to Reuters.

The 'Great American Exhibition' held on the National Mall in Washington, a key event in President Donald Trump's efforts to celebrate the anniversary, was among the activities disrupted by the extreme heat, closing temporarily on Friday afternoon amid temperatures reaching 38 degrees Celsius.

Late Friday, organizers of the Independence Day parade by the National Park Service in Washington announced they had canceled the annual event for safety reasons. The parade was scheduled to start at 10:30 a.m. Eastern Time (14:30 GMT) on Saturday, with the weather service forecasting continued high temperatures.

People walk in the streets of downtown Philadelphia after news of the cancellation of the American Independence Day parade due to the severe heat wave (AFP)

The high temperatures also strained power grids. PJM, the largest grid operator in the United States serving 67 million people, asked customers enrolled in emergency conservation programs to reduce consumption. These measures were necessary to address generator outages, overloaded transmission lines, and a sudden surge in demand for air conditioning due to the heat.

In New York, Con Edison reported that nearly 17,000 customers were without power as of late Friday evening. With rising demand, the company urged customers in New York City and Westchester County to conserve electricity.

In New York City, the city's extreme heat warning did not stop fans from gathering on sidewalks to watch celebrity guests arrive at Madison Square Garden for the wedding of pop star Taylor Swift and football player Travis Kelce.

Record temperatures spread to the eastern United States from the Midwest last week, and the National Weather Service issued heat wave warnings for more than 185 million people on Friday, with maximum heat indices potentially reaching 46 degrees Celsius in many parts of the country.

Americans gather outside a hall after news of the cancellation of the Independence Day parade due to extreme heat (AFP)

Meteorologists and government officials warned that the heat wave could be deadly, and urged Americans celebrating the Fourth of July holiday outdoors to drink plenty of fluids, stay in the shade, and watch for signs of heat-related illness at gatherings and public events.

Event cancellations were reported in at least seven states, including a major Independence Day parade in Philadelphia, as well as events in Takoma Park, Maryland and Loudoun County, Virginia.

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