Shocked ... The school serves at-risk students who were expelled or dropped out of other schools. (AP Photo/Greg Wahl-Stephens) Source: AP

Friday’s shooting outside the school in Portland was believed to be gang-related and following a manhunt police stopped a vehicle and arrested a 22-year-old suspect.

A handgun was found in the vehicle.

At the scene ... Students ran back into the school and called for help when the gunshots were fired. (AP Photo/The Register-Guard, Bruce Ely) Source: AP

The three victims - two men aged 17 and 20, and a 16-year-old girl - were rushed from the scene at Rosemary Anderson High School in north Portland. The girl was in critical condition, while the two young men were in fair condition, police said.

The victims were struck in the torso area, Portland Fire Department spokesman Damon Simmons said after the shooting, which came nearly two years to the day after the Sandy Hook school massacre in Newtown, Connecticut.

According to The Oregonian newspaper, the school is a community-based alternative establishment serving at-risk students sent there after failing to thrive in traditional high schools.

The area has been troubled by gang-related violence for years and had a spike this year. (AP Photo/Greg Wahl-Stephens) Source: AP

Nearby residents and businesses scrambled for cover as the shooting erupted.

“We heard the gunshots. We dove under the desks,” Tracy Mendoza, who works nearby, told The Oregonian, adding that she heard five gunshots.

“They were just standing on the corner at lunchtime,” she said of the victims.

The campus was locked down after the incident -- the latest in a series of shootings at schools in the United States that regularly rekindle debate about gun control laws.

In the December 14, 2012 shooting at Sandy Hook Elementary School, gunman Adam Lanza shot dead 20 children and six adults before turning the gun on himself.

On the run ... Police are still trying to track down the shooter. (AP Photo/Greg Wahl-Stephens) Source: AP