Organizers of Saturday’s Independence Day parade in Washington DC abruptly canceled the event late on the eve of the event, with sweltering temperatures in the nation’s capital and on the east coast wreaking havoc on celebrations of America’s semiquincentennial.

The event, hosted by the National Park Service (NPS), was scheduled to begin at 10.30am on Saturday. But organizers said they canceled the procession due to an extreme heart warning issued by the National Weather Service (NWS).

Blistering temperatures, exacerbated by high humidity, have been crippling transport services and stressing the electricity grid for days as the 250th anniversary of the US’s Declaration of Independence on Saturday loomed. The cancellation of the parade is just the latest setback precipitated by those conditions.

Temperatures are expected to reach as high as 102F (39C) in Washington DC today, with heat index values hitting between 110 and 115F (43-46C).

Parade organizers said they made their decision to cancel “after extensive consultation” with the NPS, Washington DC’s municipal government and the Trump’s administration, which has promoted many activities to celebrate the country’s 250th birthday.

Also affected by the temperatures has been the president’s Great American State Fair on the National Mall. That event temporarily closed down on Friday after reports that 44 visitors had been treated for heat-related illnesses.

The capital’s NBC affiliate reported that 11 people were transported to the hospital – and seven of the cases were considered “serious”.

Freedom 250, the fair’s organizer, said it would delay Saturday’s opening of the event, which has otherwise also experienced low attendances and a broken ferris wheel.

“With warm temperatures expected, guests are encouraged to stay hydrated, wear lightweight clothing, apply sunscreen, take breaks in the shade, utilize cooling areas, and look out for family and friends,” the organizing committee wrote in a social media post on Friday.

Trump is still expected to take the stage at the fair on Saturday evening to deliver a lengthy speech. His remarks will follow a packed schedule of military flyovers over the National Mall, and he will kick off a record-breaking fireworks show in the late evening.

Trump also spoke on Friday in front of South Dakota’s Mount Rushmore, taking verbal aim at the “communist menace” in the US.