One of three 12-year-old children shot at a school outside the Finnish capital has died, police say, with a 12-year-old fellow pupil suspected of the attack taken into custody.

The victims were taken to hospital, a police spokesperson told Reuters on Tuesday.

At the school, a building had been cordoned off by police and parents were picking up their children from another school building hundreds of metres away.

The arrest had happened peacefully, in the suburb of Siltamaki, away from the school.

Both the suspect and the weapon were now in police custody, police said.

There were no other suspects for now, police said.

Police officers at the scene of Viertola comprehensive school. Photo: AAP

Video circulating on social media and unverified by Reuters showed two police kneeling at the side of the suspected shooter who was lying face down on a footpath.

No details about the identities of the children or the condition of the two surviving victims were immediately released.

The shooting took place at the Viertola school in Vantaa, a suburb of Helsinki, which has about 800 pupils from first to ninth grade and a staff of 90, according to the municipality.

Anja Hietamies, the mother of an 11-year-old pupil, told Reuters she received a message from her daughter after the shooting.

“She said they were in a dark, locked classroom, not allowed to speak on the phone but could send messages,” Hietamies said, adding her daughter was scared.

Interior Minister Mari Rantanen said on X: “The day started in a horrifying way… I can only imagine the pain and worry that many families are experiencing at the moment. The suspected perpetrator has been caught.”

Prime Minister Petteri Orpo said the shooting was deeply shocking.

“My thoughts are with the victims, their loved ones and the other students and staff,” he said on X.

Previous school shootings in Finland have put a harsh focus on Finland’s gun policy.

In 2007, Pekka-Eric Auvinen shot and killed six students, the school nurse, the principal, and himself using a handgun at Jokela High School, near Helsinki.

A year later, in 2008, Matti Saari, another student, opened fire at a vocational school in Kauhajoki, in northwest Finland.

He killed nine students and one male staff member before turning the gun on himself.

Finland tightened its gun legislation in 2010, introducing an aptitude test for all firearms licence applicants.

The age limit for applicants was also changed to 20 from 18.

There are more than 1.5 million licensed firearms and about 430,000 licence holders in the nation of 5.6 million people, where hunting and target shooting are popular.

—AAP