A 15-year-old Montana girl who escaped from a mental health hospital has died after being struck by a pickup truck on a nearby interstate highway, police say.

Kayla Neal, of Missoula, was walking on the southbound lanes of I-15 around 2 p.m. Monday in Helena when she was hit by a 56-year-old woman driving a Dodge truck, police there told KURL-TV. Minutes before, she had run out of the Shodair Children’s Hospital, located about a half-mile away from where the collision had occurred.

“A Shodair patient broke the fire alarm, which caused the hospital locks to open,” Alana Listoe, the hospital's director of community relations, said in a statement distributed to local media. "The patient ran from the building and onto the Interstate and was hit by a vehicle."

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The teenage girl was treated by emergency personnel at the scene, but ultimately was pronounced dead.

A coroner told the Independent Record newspaper that Neal died from blunt force trauma.

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The investigation into her death remains ongoing and no citations have been issued.

“Administration at Shodair is cooperating with officials and providing support to staff, patients and families,” Listoe said. “Our condolences go out to the families impacted.”

Fox News' Kira Grant contributed to this report.