St. Francis Area Schools closed all of its buildings Friday and asked students and staff to stay home as police investigate a threat.

A note to students and parents posted on the district's website said police continue to investigate an alleged threat by a secondary-level student from the district.

Last week, the St. Francis Police Department investigated a threat made by a St. Francis high school student the day after a mass shooting in a Parkland, Fla., high school.

Investigators found that threat to be non-credible at the time, but increased police presence at the high school. It's not clear if that threat is related to the current investigation.

Elsewhere, on Thursday students at the Hill City School, near Grand Rapids, stayed home after school leaders said someone directed threats at some students there.

"We really, like I said, we didn't have a choice," said Pat Rendle, superintendent of Hill City School. "Based on what we were reading, there was only one alternative. They said they were going to come to school and hurt kids. We certainly weren't going to have our kids in school."

In a Facebook post, the district said law enforcement investigated the incident and determined it was a hoax.

On Thursday afternoon, the Aitkin County Sheriff's Department arrested two teenage girls in connection to the incident.

And in New Brighton, police say they've received numerous calls from parents regarding a concerning Snapchat post that was sent around to some Irondale High School students.

Authorities posted a message to the school's website Friday morning saying they believe there is no danger to anyone at the school, but more law enforcement will be present at the high school as a precaution.

The incidents follow a district-wide lockdown this week in Orono. Authorities say a high school student in the west Twin Cities metro district posted an anonymous threat to Facebook and Twitter. Police arrested the student, but did not recover any weapons.

The Hennepin County Attorney's Office has charged the boy as a juvenile.