PHILADELPHIA (WPVI) -- The birthplace of the nation is celebrating the Fourth of July and America's 250th birthday as festivities kick into high gear in Philadelphia.
However, extreme heat is forcing many event cancellations.
An Extreme Heat Warning remains in effect for the entire Philadelphia region. Temperatures in the city are expected to be around 100 degrees through Saturday.
For the latest forecast, visit 6abc.com/Weather.
Meanwhile, ABC is marking America's 250th anniversary with 24 hours of unparalleled programming called "Disney Celebrates America."
On July 4, 1776, the Declaration of Independence was signed in Philadelphia. ABC News' David Muir was in the room where it all happened - and went into the vault holding some of America's founding documents - including the printer's proof of the Declaration of Independence and the first draft of the U.S. Constitution.
Beloved actor, singer and trailblazer Sheryl Lee Ralph delivered a powerful and heartfelt rendition of the Star-Spangled Banner from beside the historic Liberty Bell in Philadelphia to mark America's 250th birthday.
The sun has started to rise on the East Coast as America celebrates its 250th birthday on Saturday.
From Philadelphia to Boston, Washington, D.C. to Raleigh and beyond, celebrations will be taking place across the country throughout the day and over the weekend.
The Philly Pops concert at Independence Mall went on Friday evening after being delayed for an hour because of extreme heat, as organizers and city public safety agencies weighed safety concerns amid sweltering conditions.
By the time the concert began shortly before sunset, conditions had improved enough for officials to allow the event to proceed.
"The heat broke a little bit," said Michael DelBene, CEO of Welcome America.
The delayed concert featured performer Idina Menzel and drew thousands of attendees to Independence Mall. While many concertgoers were eager to see Menzel perform, the dangerous heat dominated much of the day and led to the cancellation of earlier events.
"This afternoon it was really, really dangerous," DelBene said. "If we can't do it safely, we just simply won't do it."
All week amid a heatwave, Fourth of July celebrations and events tied to America's semiquincentennial have required organizers to balance public safety concerns with efforts to provide public festivities.
Those attending Friday night's concert continue to take precautions.
"I usually have my electric handheld fan and my water bottle," said Jedah Poleon of Brooklyn, New York.
Health officials warned that triple-digit temperatures and high humidity can increase the risk of heat-related illness.
"Nausea, vomiting, diarrhea, abdominal cramping and a lot of people don't equate those G.I.-type symptoms with heat illness, but that is part of the picture," said Dr. Craig Turner of Virtua Health.
Turner also advised people spending extended periods outdoors to avoid alcohol and caffeine and, in addition to drinking water, consider sports drinks containing electrolytes.
He added people experiencing symptoms should take immediate steps to cool down.
"Get out of the direct sunlight, get somewhere where you can cool off, step inside air conditioning for several minutes," he said.
Despite the heat, many attendees said they were willing to adjust their plans and continue celebrating.
"We're working around it, and we're just sucking it up and we're going for it. We're sweat warriors, we're good," said Michelle Wolfson of Gilbert, Arizona.
