The incident happened about 7.15am as students were arriving for class, Watkins told the Star Tribune of Minneapolis. After putting his backpack away, the second-grade student took out a knife and slashed three students with it, the superintendent said. School officials immediately called police and an ambulance.
By the time officers arrived, Beise said, the boy was in an office with a counsellor and the three injured students were being treated by the school nurse. He said the boy was cooperative with investigators. He said he didn't know if the boy had been bullied, or if he had mental health issues.
Beise said the boy was released to his parents. The police report will be forwarded to the Benton County Attorney's Office.
"They don't charge children this young with crimes," the chief said "You try to get them treatment and help them be successful. It's also possible that human services will become involved in some way."
In an email to parents, school officials said that the parents of the three injured students chose to take their children home or to get additional medical attention on their own.
One of the injured children is a seventh-grader who was waiting to catch a bus. The other two are Pleasantview Elementary students.
Watkins said the school made mental health counsellors available to students and staff. Classes went on as scheduled. The attacker will not be allowed back in school, the superintendent said.
Sauk Rapids is about 113 kilometres northwest of Minneapolis. Pleasantview has 720 students in kindergarten through fifth grade, according to the school district's website.
Weapons in schools and school security have been ongoing issues in the US.
A 19-year-old former student at Marjory Stoneman Douglas High School in Parkland, Florida, is accused of bringing an assault rifle to the school in February and killing 17 students and staff members. In December 2012, Adam Lanza, 20, shot his mother to death at their Newtown, Connecticut, home before killing 20 first-graders and six educators at Sandy Hook Elementary School. Lanza killed himself as police arrived at the school.
- AP