CNN  — 

A 15-year-old boy shot Monday at a junior high school in Pine Bluff, Arkansas, is in very serious condition at the children’s hospital in Little Rock, authorities said.

Pine Bluff Police Chief Kelvin Sergeant said investigators think the shooter is a 15-year-old male who is also a student at Watson Chapel Junior High.

The suspect was located in the neighborhood near the school, hiding behind a house.

He was taken into custody and is currently being held in the juvenile justice center in Pine Bluff, authorities said. Formal charges have not yet been filed.

Law enforcement outside the junior high school.

There is no known motive for the shooting, said Sergeant, who called it an isolated incident. The school followed the active shooter protocol, Sergeant said.

In a Facebook post, the school system said students were safe and schools were being locked down.

Pine Bluff is about 45 miles south of Little Rock, the state capital.

Correction: This story has been updated with the victim's correct age. The victim is 15 years old.

CNN’s Paul P. Murphy, Alisha Ebrahimji and Tina Burnside contributed to this report.