Crowds braved heavy rain to mark the US Independence Day holiday, cheering as the city's massive fireworks display lit up the sky. Crowds sporting ponchos and umbrellas stood along the river to see the 30-minute show Wednesday that was billed as the nation's biggest, with 40,000 fireworks. Eight barges on the East River and at the South Street Seaport set off an average of 1,300 shells per minute. The festivities and patriotic observances took place under heightened security in the aftermath of the attempted car bombings in Britain. For the first time, the annual Macy's show in New York featured exploding shells aimed down, not up. The shells exploded on the surface of the East River, remain illuminated for a few seconds and then fade. "Awesome!" exclaimed Ben Fedak, a New York musician taking in the show with his brother, before dazzling green shells exploded above him. "This is the best fireworks show that I've ever seen." The program featured musical performers as part of the nationally televised broadcast, including Martina McBride, Joss Stone and "American Idol" winner Jordin Sparks. Organizers estimated about 3 million people withstood the sogginess to turn out, about the same number as the year before, when another 8 million watched on national television. The organizers had called their fireworks show "waterproof." Police do not give crowd estimates. In Washington, hundreds of officers from about 20 law enforcement agencies were on duty. The National Mall open-area park was fenced off and visitors were required to pass through 19 security checkpoints, which opened at 10 a.m. Severe weather brought a tornado warning to the area, prompting authorities to evacuate the thousands of people gathered at the Mall for holiday festivities. It reopened hours later. Two fireworks crew members were injured when at least two unexploded shells went off on the ground in Washington. One had severe but non-life threatening burns, and the other was treated at the scene, authorities said. In Philadelphia, the celebrations for America's 231st birthday included a reading of the Declaration of Independence at Independence Hall, and descendants of those who signed the original document were on hand for a symbolic ringing of the Liberty Bell. Storms did not stop the fireworks show. Security measures at the New York region's tunnels, bridges and airports remained heightened following failed attacks on Glasgow and London last week, and no additional precautions beyond those already in place were taken for the holiday, said Marc LaVorgna, a spokesman for the Port Authority of New York and New Jersey. About 1,000 people from around the globe became US citizens at Walt Disney World, raising their right hands in front of Cinderella's castle at the Magic Kingdom as the oath was read by Emilio Gonzalez, head of US Citizenship and Immigration Services. "I dreamed for this moment for 13 years, and finally this is my last dream that I have," said Marta Hima, who came from Colombia and now lives in Davenport, Florida.