At least three people were shot and injured on Wednesday at an outdoor event where about 1,000 people were celebrating Eid al-Fitr in West Philadelphia, the police said.

One of those who was injured was an armed 15-year-old who was shot by a responding police officer, said Kevin J. Bethel, the commissioner of the Philadelphia Police Department.

At a news conference, Commissioner Bethel said that officers who were writing parking tickets on the outskirts of the event had responded after they heard a “large volley” of about 30 gunshots that had been fired between “two factions” in a park at about 2:30 p.m.

The three people who were injured were in stable condition, he said. One was a 22-year-old who was shot in the stomach. Another was a young person who had a gunshot wound in the hands, he said. And one was a 15-year-old who was shot in the shoulder and leg by a police officer. Commissioner Bethel said the teenager had a gun.

After the 15-year-old was shot, the officer who shot him drove him to the hospital, Commissioner Bethel said. That teenager was one of five people who were arrested, he said, adding that the police had recovered four guns.

A child was also struck by a police vehicle and had a fractured leg, he said.

Commissioner Bethel did not describe a motive, but he commended those who responded for helping to usher children to safety after the shooting, which was near a mosque, the Philadelphia Masjid.

“I walked through this event and we know the majority — 99 percent of the individuals — at this event are good people who wanted to have a good time,” Commissioner Bethel said. “And once again, we have young people engaging in gunfire who really destroyed the sanctity of what happened.”

He said that Mayor Cherelle Parker was reaching out to the Muslim community to ensure they had support.

A witness who attended the event, Saul Landers, said there was a “friendly vibe” with people playing games, riding horses and enjoying free food. Then he said he heard about 15 shots and saw “everybody running and taking cover.”

“It was sad, heartbreaking,” Mr. Landers said.

Jamie R. Gauthier, a member of the Philadelphia City Council, said she attended the event in the morning and saw families coming together to celebrate the end of Ramadan. “It was so joyful and such a beautiful day,” she said.

She said the shooting pointed to the need for greater gun control. “These young people should not have had access to the weapons they did that enabled terror at what was supposed to be a joyful religious celebration,” she said.