Image copyright Getty Images Image caption US classroom (file image)

Two teenage girls have been arrested in the state of Florida for allegedly planning to murder nine people, US media report.

The pair from Avon Park Middle School, both aged 14, were arrested on Wednesday after a teacher found a folder detailing their alleged plans.

In eight sheets of notes, the girls allegedly laid out plans to obtain guns and move and dispose of the bodies.

They are both being held in custody, pending a trial hearing.

Each suspect faces nine counts of conspiracy to commit murder and three counts of conspiracy to commit kidnapping.

The teacher reportedly noticed the girls acting "hysterical" whilst looking for the folder, and allegedly overheard one of them say "I'm just going to tell them it's a prank if they call me or if they find it".

The teacher later found the folder, which had been labelled as "Private info", "Do not open," and "Project 11/9".

Inside, handwritten notes outlined a list of names and included detailed plans about how to carry out the killings, according to the broadcaster NBC.

The documents talk about obtaining firearms and destroying evidence by burning and burying their victims' bodies.

Another note also addressed what clothing the teenagers would wear for the task.

"NO NAILS," it reportedly read.

"NO Hair Showing from the moment we put on our clothes".

"It doesn't matter if they thought it was a joke," said Scott Dressel, spokesperson for Highlands County Sheriff's Office, quoted by Fox47 news channel.

"There's no joking about something like this. You don't make a joke about killing people."