The National Football League announced a new partnership with TikTok, including plans to sell ads together so brands can sponsor the league’s content and hashtags on the Chinese-made mobile video app.

On Tuesday, the NFL unveiled an official TikTok account that accumulated almost 260,000 fans by midday. It also proliferated the hashtag “we ready,” which was meant to inspire users to share videos of how they prepare for opening day on Thursday.

The NFL has been talking with TikTok for the past several months about a formal partnership, says Blake Stuchin, VP, digital media business development for the NFL. “We’re always following the market landscape and looking at new products to continue to challenge ourselves and innovate,” Stuchin says, adding that the league has been interested in TikTok “going back to Muscial.ly.”

TikTok’s owner ByteDance bought Musical.ly in 2017. Both apps catered to lip-syncing users showing off their musical interests in short videos. Now, just TikTok, the app has expanded into a more general-interest video app, where users and brands congregate around hashtags. Sponsored hashtags were TikTok’s first ad product, debuting with Guess jeans last year.

The app has since expanded into more traditional video ads and product integrations with e-commerce components, so users can buy what they see in videos.

The NFL did not disclose the terms of the deal, only saying that it’s a multiyear partnership. The league did not pay to promote the "we ready" hashtag, but plans on sponsoring hashtag challenges in the future, Stuchin says.

“We’re programming content every day on TikTok,” Stuchin says. “The NFL and TikTok will be creating elements that advertisers will be able to sponsor. That could be sponsored hashtags that include brands as part of the challenge. It may involve NFL content published on TikTok that could have brands integrated into it.”

In recent years, the NFL has sought out new social-media platforms as a way to go after younger audiences who may not be tuning to live games as frequently as previous generations. Young viewers, 18- to 34-year-olds, spend less than two hours a day watching TV and three and a half hours on their phones, according to a recent Nielsen report.

The league has relationships with Twitter, Snapchat, YouTube and Facebook. TikTok is unique in that it’s the first major social-media platform to originate from China and find success in the U.S.

TikTok has never revealed daily user stats, but the app has been downloaded more than a billion times. Stuchin says, according to the stats he’s seen, most of the audience is under 24 years old and spends up to 50 minutes a day on average watching videos.

The NFL plans to tell stories in a “fun, irreverent way,” Stuchin says, and true to the app’s roots, many of them will be “musical in nature.”

TikTok is only getting started with professional sports, too. La Liga, the Spanish soccer league, joined in May.

“We've seen this fast growth across football content and broadly with sport content on TikTok,” a spokeswoman for TikTok said by e-mail. “Partnering with leagues like NFL gives the global TikTok community a peek inside a world they might not see every day, and we're looking forward to working closely with them and seeing the exciting content and experience they bring to the platform.”

—Anthony Crupi contributed to this story