US authorities have arrested six teenagers, including a 14-year-old, over a drive-by shooting outside a school that killed a 15-year-old boy and seriously wounded two female teenagers.

The suspects, all from Des Moines in Iowa, are charged with first-degree murder and two counts of attempted murder after the Monday afternoon shooting in the grounds of East High School, near central Des Moines.

Police said gunshots fired outside the school came from several people in multiple vehicles.

Officers named the suspects as Octavio Lopez, 17, Henry Valladares-Amaya, 17, Manuel Buezo, 16, Romero Perdomo, 16, Alex Perdomo, 15, and Nyang Chamdual, 14. All are from Des Moines.

Police said the 15-year-old who was killed was not a student at the school, but was the intended target of the attack.

The other two victims were females aged 16 and 18, who both attend East, and were bystanders caught in the shooting, police said.

Officers said the 16-year-old girl remained in hospital in serious condition, while the 18-year-old was in critical condition.

Sgt Paul Parizek told KCCI-TV that calls started pouring in around 2.50pm on Monday, shortly before classes were scheduled to end for the day.

School Shooting Iowa
Police at the scene (Zach Boyden-Holmes/Des Moines Register/AP)

The district said in a news release that the school was immediately put into lockdown and students were kept inside while police investigated.

The lockdown ended at around 3.30pm after law enforcement gave an all-clear.

School principal Jill Versteeg described what happened as “everyone’s worst nightmare” and urged parents to “hug your students and love them”.

The district said there would be no classes on Tuesday and college admissions test and parent-teacher conferences were being cancelled. The district was also making grief counsellors available.

Superintendent Thomas Ahart said school shootings have “become too common” and that “real change to gun laws and access would go a long way to help us”.

He added: “Our staff and students are forced to train for these incidents and the trauma associated with the repeated drills and incidents will remain with them for years to come.

“It’s unfortunate that our state and our country have become a place where firearms are far too easily accessible.”

Police said they do not believe there is a continued threat to the public. A motive was not immediately known.

Authorities have recovered shell casings from the scene as they investigate what happened.

Des Moines Police Chief Dana Wingert went to the school after the shooting and expressed frustration at the violence.

“Unfortunately what happened here today was just another pointless tragedy in our community,” he told TV station WOI-TV. “People using firearms to settle their differences.”

Police said it was the fourth homicide in Des Moines this year.