The atmosphere created by some young people Thursday in Riverside Park during the Independence Day festivities turned as combustible as the fireworks.

Groups from outside the neighborhood, according to witnesses, started a number of fights and later wreaked havoc on Tonawanda Street by blocking traffic and jumping on cars before they were dispersed without arrests.

“It was a rough crowd,” said Annette Class, a Riverside resident who attended with her three children.

She was upset by both a fight that broke out in the front of the crowd during the fireworks show and also the behavior of some young people afterward.

“I think next year we’ll just watch it from our house,” she said. “It wasn’t a crowd I would want my children in, and I wouldn’t suggest it for anyone with younger children.”

A Buffalo police officer, who asked not to be named, confirmed some fights at the Friendship Festival, which includes carnival rides. The biggest problem was the crush of people that made it difficult to leave after the fireworks concluded.

The Police Department estimated the crowd at 20,000.

Making matters worse, the officer said, was a large group that briefly took over a street surrounding the park. “They all went on Tonawanda Street and they didn’t go home. They blocked traffic, they stood in the middle of the street, they were jumping on people’s cars. We just moved them out and got rid of them,” said the officer, who was not authorized to speak to the media.

A large fight between women broke out during the evening, and a North Buffalo woman reported that several women jumped her.

Michael Moody, a carnival ride operator, said a fight broke out near the Sea Ray ride, a day after he witnessed a fight by the Orient Express that he said involved an estimated 45 young people.

Despite the violence, only one arrest was made Thursday. Police arrested a 20-year-old man on an illegal weapon possession charge, said police spokesman Michael DeGeorge.

Marlek Williams, of Littlefield Avenue, was arrested after police chased him from Hertel Avenue and Tonawanda Street to the second block of Gorton Street at about 11 p.m. Police found a loaded .380-caliber handgun he allegedly threw over a fence just before they caught him.

He was charged with obstruction for refusing to talk to officers at Hertel and Tonawanda, where they had responded to a “man with gun call.”

A day earlier, during the festival, Justin Smith, no age available, of Ontario Street, was arrested for pulling out a knife during a fight.

Council Member Joseph Golombek Jr. said that besides “a handful of isolated fights,” the event had far fewer problems than last year’s festival, during which he said young people from outside the neighborhood were disruptive. The officer who spoke to The News agreed.

Crystal Best, who lives on Tonawanda Street, said she thought the sheer size of the crowd overwhelmed the ability of the police to respond to some of the problems that flared.

“There were just too many people for them to control,” Best said. Additional police officers were added Friday, even though attendance was smaller than the night before.