A crowd of determined festival goers just stormed Lollapalooza, jumping the fence en masse to get in.

Photographer Jeremy Cohen, who's shooting the event, caught the phenomenon on video. In a Twitter DM to Mashable, he said he saw the mob "casually walk down the street."

"When they saw a spot with not many cops around, they stormed the gate all at once," Cohen said. "It was def planned ... [It] was very strategic."

He's photographed many music festivals, but added that he's "never before" seen anything like this.

In the video he posted, which is quickly going viral on Twitter, police were only able to stop one kid, who has a prosthetic leg.

Tweet may have been deleted

Other Twitter users, including YouTuber Casey Neistat, rallied in support of the boy who didn't make it over the fence.

Tweet may have been deleted

Tweet may have been deleted

Tweet may have been deleted

Some joked that it was a test run to storm Area 51.

Tweet may have been deleted

Tweet may have been deleted

Tweet may have been deleted

Cohen said he wouldn't be surprised if this was the result of a Facebook event similar to the infamous one prompting people to "storm Area 51." He also noted that they could have organized through a private group or Discord server — whatever platform they used, it definitely wasn't a spontaneous hive mind decision, but planned collective action.

"I think this was just a practice sesh for Area 51," Cohen continued. "All you need is good shoes and power in numbers."

The Chicago Police Department has not responded to request for comment.