The Department of Homeland Security is urging schools to stay vigilant Friday amid unfounded threats of violence spreading on social media.

       "DHS is aware of public reporting that suggests possible threats to schools on December 17, 2021," the agency tweeted Friday morning. "DHS does not have any information indicating any specific, credible threats to schools but recommends communities remain alert."

       In New York City, the NYPD said Thursday the department was aware of "posts circulating on TikTok concerning a potential school shooting on Friday," but there was "no credible information to suggest this threat is specific to any school in New York City."

       The NYPD said it was sending extra resources to NYC schools as a precaution.

       The Washington Post via Getty Images, FILE

       School resource officers walk through a hallway at T.C. Williams High School on June 09, 2021, in Alexandria, Va.

       Other schools have closed due to the threats. In Wisconsin, the Platteville School District said it canceled school Friday due to a potential threat of violence.

       Jake May/The Flint Journal via AP, FILE

       Handwritten messages are left at a memorial site outside Oxford High School after a deadly school shooting, in Oxford, Mich., Dec. 7, 2021. School officials around the country are planning to step up security Friday in response to social media posts warning of violence on TikTok.

       In California, the Los Angeles Unified School District said classes will be in session Friday despite the threats.

       "There is no reason to believe our schools are in any danger," the district said Thursday.

       Santa Monica police said they'll be highly visible at schools Friday even though there aren't specific threats.

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       The FBI's Los Angeles field office said, "While we continue to monitor intelligence, we are not aware of any specific threats or known credible threats to schools in the Los Angeles region at this time."

       TikTok said it's "working with law enforcement to look into warnings about potential violence at schools even though we have not found evidence of such threats originating or spreading via TikTok."

       The DHS said it'll continue to monitor the threats and asked people to report suspicious activity to law enforcement.

       ABC News' Josh Margolin, Luke Barr and Ahmad Hemingway contributed to this report.