Three young children and a teacher have been killed after a 16-year-old gunman opened fire at a school in the US state of Oregon.

Police in Bend – a city of about 100,000 residents – said the first report they received was from someone in a vehicle who said they had been shot at multiple times by a person with a long gun.

“In the ensuing several minutes, dispatch received dozens of 911 calls reporting that a shooter had entered the building at Silver Rail Elementary School,” Police Department chief Mike Krantz told reporters.

Krantz, who described the shooting as a “terrible tragedy”, confirmed that three children aged five, eight and 11 had been killed, along with a teacher.

A seven-year old child and another teacher were taken to hospital with critical injuries.

The suspect, later identified as a 16-year-old Bend resident, was shot dead by a community member who had “pursued him into the school and engaged him”, Krantz said.

Silver Rail Elementary School was put into immediate lockdown, with all students and staff eventually transported to a nearby school to be reunited with their families.

Bend-La Pine Schools superintendent Steven Cook said its immediate priorities were caring for students and staff, and helping law enforcement and emergency responders.

“We are stunned and heartbroken by this senseless tragedy,” Cook said.

“We extend our deepest sympathy to the families and to everyone affected by this violence. No words can adequately express the grief our community is experiencing.”

Krantz, who said Bend officers had recently undergone “active threat training” at a local high school, said there would be a large police presence at the elementary school for several days.

He warned the investigation into the shooting would be a long one.

“This is something we never want to happen anywhere, but especially and particularly in our beautiful community here in Bent,” he said.

“There are not really any words I can say to any of you that will make this better… we know this deeply impacts the community and ask everyone to be there for each other and lean on each other.”

–with Reuters / AP