A 16-year-old gunman reportedly killed a teacher and four children at an elementary school in the US state of Oregon on Thursday before an armed bystander shot him dead, police said.

The incident occurred at Silver Rail Elementary School in Bend, a city of about 100,000 people in the northwestern United States, after police received reports of a shooting on the school premises on Thursday afternoon.

The United States, where firearms are widely available, has a long history of gun violence, with thousands of people killed annually. The country has one of the highest rates of gun-related deaths among developed nations.

On Thursday evening, residents gathered at Drake Park in Bend for a candlelight vigil to honour the victims.

“I’m in total complete shock, and scared and sad,” said a woman identified only as Betsy, who spent about 10 minutes standing near a circle of candles and flowers.

“It’s awful, but it also has brought people together,” she told AFP.

Police Chief Krantz told journalists that the department first received a report of an active shooter after a caller said someone carrying a long gun had shot at them several times.

Dozens of emergency calls subsequently reported that the gunman had entered the school, prompting law enforcement officers across the area to respond to the scene.

Officers arrived at about 1:02 p.m. local time (2002 GMT), within minutes of receiving the reports, the police chief said.

“Moments later, an officer reported that the suspect had been shot by a community member who had seen the suspect enter the school and pursued him into the school and engaged him,” Krantz said.

“Our officers entered the building and confirmed the suspect was dead.”

Police said a seven-year-old child and a 54-year-old teacher, both critically injured, were transported to a local hospital.

The police chief said the investigation was still in its early stages but indicated that the gunman appeared to have forced his way into the school by shooting at locked doors.

He added that the 16-year-old suspect was a resident of Bend.

According to a police spokesperson, between 400 and 450 children attend Silver Rail Elementary School, which employs more than 40 staff members.

Following a lockdown, the Bend-La Pine School District said law enforcement officers were escorting students on buses to a separate location where they could reunite with their families.

The district’s superintendent, Steve Cook, tearfully described the incident as “an unthinkable tragedy.”

“We are heartbroken. We are horrified. This is the kind of thing you hear about in other places, and pray that it never happens here,” he told reporters.

Parents anxiously waited at a nearby church as students were transported to the reunification centre.

Drew Sharp, the father of a fifth-grade pupil, told CBS News: “I have faith that he’s okay and that he’ll be alright.”

He said the children were disembarking from the buses from the youngest to the oldest, adding that although the arrangement made sense, “it’s just more time waiting.”

The Bend-La Pine School District announced that classes across the district would be cancelled on Friday, alongside other school activities and sporting events.

Silver Rail Elementary School is located approximately 170 miles (270 kilometres) southeast of Portland. The school serves children from kindergarten through fifth grade.