A 16-year-old boy opened fire at an elementary school in Bend, Oregon, killing three children and a teacher before being shot dead by a bystander who pursued him into the building.

Police were alerted to an active shooter at Silver Rail Elementary School at 12:59 local time (19:59 GMT), according to a spokeswoman for the Bend Police Department.

The first emergency call came from a person who reported that an unknown suspect was firing into their car with a long gun. Photos released from the scene show a red truck with bullet holes.

Minutes later, the local county dispatch received 911 calls reporting that the attacker had entered the school. Police said he shot at door locks in order to force his way inside.

Local media reports suggested the school had received new classroom doors in 2022 that can be locked with the flip of a switch.

A bystander who witnessed the shooting begin to unfold pursued the attacker into the school and shot him dead, police said. Officers arrived at the scene three minutes later, confirmed the attacker had been killed, and then searched the building.

Police identified the attacker as a local 16-year-old boy but did not release further details about him or the identities of the victims.

"We are stunned and heartbroken by this senseless tragedy," said Steven Cook, the top administrative official of the local school district, in a statement. "No words can adequately express the grief our community is experiencing."