Two children aged eight and 10 have been killed and 17 people injured when a gunman opened fire on schoolchildren attending Mass at a Catholic school in the United States, authorities say.

The police chief of Minneapolis, Minnesota, said that of the people injured in the Wednesday morning attack, 14 are children and two are in critical condition. Authorities have not yet discerned a motive for the attack and said the suspected gunman – armed with a rifle, a shotgun and a pistol – took his own life.

“This was a deliberate act of violence against innocent children and other people worshipping,” Minneapolis Police Chief Brian O’Hara said during a news conference. “The sheer cruelty and cowardice of firing into a church full of children is absolutely incomprehensible.”

Police said the assailant was in his 20s and did not appear to have had an extensive criminal history. Dozens of rounds were fired during the attack, during which the gunman, dressed in black clothing, stood outside the church and fired in through the windows as schoolchildren were seated in the pews.

“I’m praying for our kids and teachers whose first week of school was marred by this horrific act of violence,” Minnesota Governor Tim Walz said in a social media post.

Children’s Minnesota, a local hospital system, said it admitted at least five children.

“I was shocked. I said, ‘There’s no way that could be gunfire,’” Bill Bienemann, who lives nearby and has long attended Mass at Annunciation Church, where the shooting took place, told The Associated Press news agency.

“There was so much of it. It was sporadic.”

US President Donald Trump described it as a “terrible situation”.

“I have been fully briefed on the tragic shooting in Minneapolis, Minnesota,” Trump said on his Truth Social network.

“The FBI quickly responded, and they are on the scene. The White House will continue to monitor this terrible situation. Please join me in praying for everyone involved!”