Officials speak to people at the scene of a shooting at Rosemary Anderson High School in North Portland. (AP Photo/The Register-Guard, Bruce Ely) Source: AP

The victims are believed to be students at Rosemary Anderson High School in the north-western city of Portland, Sergeant Pete Simpson said.

The three were conscious and breathing when they were taken to the hospital, he said.

The shooting was reported after noon and happened at a corner outside the school.

A group of students leave Rosemary Anderson High School in Portland after a shooter hurt three students. (AP Photo/Greg Wahl-Stephens) Source: AP

The assailant fled, and the students ran back to the school for help, he said.

Officers don’t know whether the shooter was alone or with others, but Simpson says preliminary information suggests it is gang-related.

Rosemary Anderson High School is an alternative school that serves at-risk students who were expelled or dropped out, are homeless or single parents.

According to the school’s website, 190 students annually are enrolled there.

Parents have been summoned to the school, and a nearby high school and community college were put on lockdown.

Parents and teachers gather outside Rosemary Anderson High School following a shooting at the alternative school. (AP Photo/Greg Wahl-Stephens) Source: AP

Portland has been troubled by gang-related violence for years and had a spike this year.

At midyear, the Police Bureau reported that officers had responded to 52 gang-related violent crimes, up from 35 through the same period last year, The Oregonian reported.

Some of the violence occurs between rival gangs, but bystanders have also been hurt.

Two men died in separate gang-related shootings earlier this year, including one outside a strip club.

Portland Police near Rosemary Anderson High School investigate the alleged gang-related attack. (AP Photo/The Register-Guard, Bruce Ely) Source: AP

In another shooting in June, at least nine gunshots were fired into an apartment complex, and a five-year-old boy who was visiting his grandfather was wounded in the leg.

Portland police have been calling for more resources to deal with the gang problem.

The Portland area was the scene of a school shooting in June.

Jared Padgett, 15, opened fire June 10 after arriving at his high school east of Portland heavily armed. He killed 14-year-old Emilio Hoffman in the boy’s locker room and another bullet grazed a physical education teacher. When confronted by officers, Padgett went into a bathroom and died from a self-inflicted gunshot, police said.

Terence Lewis, right, with Alexis Lewis, centre, and his mother leave Rosemary Anderson High School after the shooting. (AP Photo/Greg Wahl-Stephens) Source: AP