Two schoolgirls are facing charges of plotting mass murder in the US after a teacher allegedly found their detailed written plans to kill nine people.

Kept in a folder labelled "private info", the plot detailed how the girls, both 14, would obtain guns and kill their victims, before "burning and burying their bodies", according to an official incident report seen by local media in Florida.

The plans were named "Project 11/9" and included details on what the girls would wear, Fox 13 reported.

A teacher at the teenagers' school, Avon Park Middle School, initially grew suspicious after seeing the girls in a classroom acting "hysterically" in search of the folder, according to court documents reported by WTSP-TV.

They were overheard discussing how its contents could get them arrested, before one girl suggested she would tell police it was just a joke.


The teacher eventually found the folder and raised the alarm with school authorities.

In a Facebook post on Thursday afternoon, the Highlands County school board said the two students had been taken into custody, and their families informed.

Both girls were later charged with multiple counts of planning to commit murder and kidnapping.

It is not yet known whether they will be tried as adults.

A statement quoted in local media from the deputy superintendent of Highlands County Schools, Andrew Lethbridge, reminded students that they are responsible for their words.

"We are all held accountable for the information that we communicate," he said.

"The [school board] takes threats very seriously and we work closely with the [Highlands County Sheriff's Office] to investigate them."