School districts across Massachusetts alerted families Thursday to a vague threat about school shootings on Friday, Dec. 17, that was reportedly shared on the social media app TikTok. The districts emphasized that they were not aware of any specific or credible threats to their schools, but that they were still taking it seriously.

The messages originated from Natick, Holliston, Belmont, Cambridge and Cohasset. Many said that they will have an increased police presence at their schools on Friday as a precaution.

“We understand that students can be influenced by social media. It is always important to remain vigilant when it involves these types of threats,” wrote Cambridge Public Schools Superintendent Victoria Greer.

Massachusetts schools were not the only ones to react: school districts across the country sent out messages to their families, and at least one, Gilroy High School in northern California, will shut its school buildings altogether on Friday.

School officials in states including Arizona, Connecticut, Illinois, Montana, New York and Pennsylvania said Thursday there would be an increased police presence because of the threats.

“At this point in time we are not aware of any credible threats to schools in Massachusetts,” Kristen Setera, with the FBI Boston field office, told MassLive. “The FBI takes all potential threats seriously and we regularly work with our law enforcement partners to determine the credibility of any threats. As always, we encourage the public to remain vigilant and to report any suspicious activity to law enforcement immediately.”

TikTok responded to the post Thursday, saying it responded to all threats, even rumored threats, with “utmost seriousness.”

“We're 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 company wrote in a statement on Twitter.

Massachusetts superintendents urged families to talk about what they see on social media and to speak up if they see something that doesn't look right.

“Please take some time to talk to your child about the pressures of social media,” Cambridge’s Greer wrote. “Please reiterate that everyone has a responsibility to share information related to the safety of our school community with the administration or a trusted adult immediately.”

“If you use these viral social media challenges as an opportunity to talk about digital citizenship with your students, this can be a way to bring up how social media impacts and shapes our identities—and how it shapes the way others might see us, too,” wrote Natick Public Schools superintendent Anna Nolin.

This article includes reporting from the Associated Press.