Two 15-year-old girls died Friday in a shooting at an Arizona high school that initially caused panic among parents who could not reach their children but later was revealed to be a likely murder-suicide.

Authorities announced that a suicide note was found at the shooting scene near the cafeteria area of Independence High School in Glendale. They said the girls each were shot once, were declared dead at the scene and a weapon was found near the bodies.

"Information gathered by detectives reveal the two girls were very close friends, appeared to also be in a relationship," Glendale police spokeswoman Tracey Breeden said in a statement Friday afternoon.

Arizona School Shooting

A police officer gives instructions to parents waiting to be reunited with their children on Friday in Glendale, Ariz., after two teens died of gunshot wounds at Independence High School in the Phoenix suburb. (Matt York/Associated Press)

Breeden said it is believed nobody witnessed the shooting.

Both teens have been identified, but Breeden said "their names will not be confirmed or released at this time by the police department due to their juvenile status."

Hours before the lockdown of the school was lifted, hundreds of worried parents crowded the parking lots of nearby discount and convenience stores.

Social workers and counsellors will be available to students and staff when school resumes Tuesday, Glendale Union High School District Superintendent Brian Capistran said.

Arizona Gov. Doug Ducey tweeted his sympathies, saying, "Our prayers are with the students, educators & families at Independence High School & all the first responders on the scene."