After chaos broke out in Union Square Park, a YouTube streamer was charged with inciting a riot.

Kai Cenat, a popular YouTube, and Twitch streamer, said he would give away free game consoles in a park in Manhattan. This made a lot of people go there.

When the police went to Union Square Park to deal with a big crowd, they arrested an unknown number of people. Credit… For The New York Times, Jeenah Moon

On Friday, a popular social media streamer was charged with starting a riot after an event in which he planned to give away video game consoles turned into chaos and drew an estimated crowd of several thousand young people.

At a news conference late Friday, the head of the Police Department, Jeffrey Maddrey, said that the live streamer, Kai Carlo Cenat III, was likely to be charged with unlawful assembly and, possibly, other crimes.

The trouble started around 3 p.m. and was mostly over by 6 p.m., with 65 arrests (almost half of them of juveniles), injuries to officers and some people in the crowd, and damage to food carts, police vehicles, and stores, according to officials.

Among all the chaos, some people set off fireworks. Credit… The New York Times’ Victor J. Blue

“It was out of hand. It took some time before we could handle it. And many young people got hurt,” Chief of Department Jeffrey Maddrey said at one of two news conferences held after the park was cleaned up. He was speaking in front of a trash-filled plaza.

Mr. Cenat and another streamer, Fanum, said they would be at the park at 4 p.m. to give away PlayStation 5 consoles. The two are part of the streaming group AMP, which has a lot of fans on YouTube and the streaming site Twitch. More than 3.6 million people watch videos on Mr. Cenat’s YouTube channel.

Chief Maddrey said the event was unplanned and happened without a city permit. A post on social media around noon told the police about the meeting, he said. He said that by 3 p.m., the post had “gone viral.”

At that point, he said, “The event got bigger, faster, and bigger.”

Soon, there were so many young people in the park that they crowded the streets and sidewalks around it, making it hard for cars and people to get through. The popular Greenmarket in Union Square closed early. Trains started to go around the Union Square station.

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As 4 p.m. got closer and the crowd got more agitated, the Police Department started a Level 4 mobilization, which is its highest level of response. Some people in the crowd stayed calm, but others got out of hand. The chief said that a group of people broke into a construction site and started throwing building materials, rocks, and bottles at each other.

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He said people were walking around with shovels, axes, and other building tools, and others were lighting fireworks and throwing them at officers and each other.

When the time for the giveaway came and went, the chaos got worse.

Water bottles, basketballs, a computer, and fireworks hit the crowd. When police with riot shields tried to arrest a group of young people, another group pushed them back. Over 200 people crowded around a flagpole in the park and chanted something rude at the police. People were seen climbing on top of cars stuck in the crowd.

By early evening, most of the people had left. Credit… For The New York Times, Jeenah Moon

Chief Maddrey said that people in the crowd started to “do violent things to the police and the public.”

“A lot of these young people didn’t do what we told them to,” he said. “They wanted to see this influential person very much.”

By 5 p.m., most of the crowd was on Park Avenue, where hundreds of young people were blocking both lanes, banging cars, and throwing things. Those who didn’t move up the street when told to were tackled and put in jail.

A teenager yelled at an officer, “That’s my friend. You’re going to jail!” “He’s my kid.”

“You also want to go to jail?” After the officer answered, he grabbed the teenager, put him on the ground, and put zip-tie handcuffs on him.

Several helicopters hovered above as the police pushed a group of young people up the street, one block at a time, every few minutes.

At 19th Street, a group driving north took a knee and started chanting “Black Lives Matter.” At 20th Street, they sat on wicker chairs outside a fancy restaurant while workers locked the doors and watched from inside. Dozens of teenagers rushed into a CVS store on the 22nd and grabbed water bottles, candy, and snacks, which they gave to other people in the crowd.

“When we started getting rid of the young people here, they ran through the city streets and stole plates from people who were eating outside,” said Chief Maddrey.

The chief said the crowd was given several chances to leave before any arrests were made. Some of the people who were being held by police were put on a city bus, which was attacked as people tried to free those who were being taken away.

Chief Maddrey said that Mr. Cenat was taken to safety and that police were considering whether to charge him with “inciting a riot.”

He said, “This shows how powerful and dangerous social media can be.”

Josh Ortiz, who lives in the Brownsville neighborhood of Brooklyn, was one of the people in the crowd. He said he was at the park to see the two YouTube stars.

“I just came out to see them,” Mr. Ortiz, who is 18 years old, said. “I think many kids thought they could get a free PC or PlayStation and start making money, but I just wanted to see Kai. He is the most famous Black artist in the United States.”

He said that at first, everything was calm, but a few people had “gone crazy.”

He said, “It’s somewhere between annoying and funny.” “There was a big explosion just now, but it’s kind of funny if you know, like I do, that it’s just kids with fireworks.”

Mr. Ortiz said that Mr. Cenat was to blame for some of the chaos.

“It’s kind of Kai’s fault,” he said, adding that the event “wasn’t well planned” and that Mr. Cenat could have picked “a more open area.”

As the situation in the park worsened, a large group of teenagers rushed to the front door of the Best Buy store nearby, making the employees lock the doors.

“These guys are huge,” said Zap, a 21-year-old gamer from Queens who didn’t want to give his real name. He said 90,000 people were watching Mr. Cenat’s live stream when he told them about the giveaway a few days ago.

Adam Mass, a student from Brooklyn who is 20 years old, said he came to the park after hearing about the chaos.

Mr. Mass, who called the two streamers a “big deal,” said, “I heard they were out here.”

He also said, “I didn’t even want a freebie.” “I knew, though, that something was happening, so we came here.”