NEW YORK: Americans marched in star-spangled parades, ran relay races, gathered for fireworks shows and crowned a new world hotdog eating champion as they celebrated Independence Day in traditional style yesterday.

Possible security threats, wildfires in the West and rainy weather on the East Coast apparently did little to dampen the spirits of celebrants decked out in red, white and blue from their headbands to their shoelaces.

Crowds at Boston's Old State House erupted in applause and cannons shot out tri-colour confetti after the annual July Fourth reading of the Declaration of Independence.

Later, thousands flocked to the Charles River Esplanade for the annual Boston Pops concert and fireworks.

The crowd in Washington, DC, watched a parade of brass bands, law enforcement motorcycle units, high school drum majorettes, antique cars and police and military detachments.

The National Mall, an open area west of the Capitol and site of a fireworks display expected to draw hundreds of thousands, was soggy from steady rain that had stopped by the time the parade started.

The Department of Homeland Security and the Federal Bureau of Investigation issued an alert this week asking local authorities and the public to remain vigilant for possible threats following recent calls for violence by leaders of radical Islamist group Islamic State.

In New York City, the nation's biggest police force assigned about 7,000 officers and nearly all its counterterrorism personnel to handle security around Independence Day events.

Even after promising an increased presence at weekend events, Massachusetts State Police maintained a holiday spirit, tweeting with a colloquial Boston phrase early Saturday "Have a wicked safe 4th of July!"

In a stunning upset on Coney Island, 23-year-old newcomer Matt Stonie grabbed the famed mustard-coloured champion's belt after gobbling 62 hot dogs in 10 minutes in the annual Nathan's International Hot Dog Eating Contest. Stonie, of San Jose, California, ousted long-time champion Joey "Jaws" Chestnut, who still holds a world record of 69 franks eaten in 2013. Miki Sudo hung onto the women's title, downing 38 hotdogs in 10 minutes.