Splashy fireworks set off in N.Y.

Tens of thousands of people braved heavy rain to mark the Fourth of July holiday, cheering as the city’s massive fireworks display lit up the sky and for the first time seemed to set the East River’s surface aflame.

Crowds sporting ponchos and umbrellas stood along the East River to see a formation dubbed the Jellyfish, which resembles the underwater creature, and the Electric Rice Krispies, crackling metallic shells.

For the first time, the annual Macy’s show featured exploding shells aimed down, not up.

The shells exploded on the surface of the East River, remained illuminated for a few seconds and then faded.

“Awesome!” exclaimed Ben Fedak, a Queens musician watching the show with his brother. “This is the best fireworks show that I’ve ever seen.”

The 30-minute show was billed as the nation’s biggest, with 40,000 fireworks.

Eight barges on the East River and at South Street Seaport set off an average of 1,300 shells a minute.

The program, broadcast on television, featured musical performers, including Martina McBride, Joss Stone and “American Idol” winner Jordin Sparks.

Organizers estimated about 3 million people withstood the foul weather to turn out, about the same number as last year. The organizers had called their fireworks show waterproof.

However, the threat of storms forced officials in several eastern Pennsylvania cities to postpone fireworks shows.

And dry weather curtailed celebrations in some locations, including Breckenridge, Colo., where there was a high fire danger.

The festivities and patriotic observances took place under heightened security in the aftermath of the attempted car bombings in Britain.

Security measures at tunnels, bridges and airports in the New York region remained heightened after last week’s failed attacks in Glasgow, Scotland, and London, said Marc La Vorgna, a spokesman for the Port Authority of New York and New Jersey. No additional precautions beyond those already in place were taken for the holiday, he said.

In Massachusetts, 20 local, state and federal agencies were assigned to help police at the Boston Pops concert and fireworks show. Car and boat traffic were banned from the area.

In Philadelphia, the holiday began with a reading of the Declaration of Independence at Independence Hall.