Authorities in the city of Everett, Washington have arrested an 18-year-old after a tip off from his grandmother led them to believe he was planning to shoot his classmates.

Police said that on Tuesday 13 February a grandmother in Everett called 911 because she believed her grandson was planning on shooting students at ACES high school in the city.

Officers attended the grandmother's house, the city's police department said, where they were shown excerpts from the teenager's journal.

The journal so alarmed the officers that the high school was contacted to alert them to the threat that the teenager might pose.

Police said that the journal detailed plans to shoot students and use homemade explosive devices at the facility, they were also said to be alarmed by statements made in the journal.

The grandmother had also reported that her grandson had a rifle which was stored in a guitar case. The grandson was arrested at the school.

Police said that on his person during the arrest officers found marijuana and a knife. Authorities said that he was booked into Snohomish County Jail on probable cause for attempted murder "due to planning and taking substantial steps toward executing a school shooting."

Major Crimes Unit detectives served a search warrant at the grandmother's house to seize the journal, rifle and military style inert grenades, along with other evidence.

America continues to discuss gun culture and control in the country after a shooting at a Florida high school killed at least 17 people. Broward County Sheriff's Office said in a report that 19-year-old Nikolas Cruz had confessed to the shooting at Marjory Stoneman Douglas High School.

Cruz's attorney told reporters that he was remorseful and is aware of what is going on but that he's a "broken human being".