A truck was driven into a youth football game in Wichita, Kansas, leaving a six-year-old boy and a 35-year-old man dead, and 10 others hospitalised with traumatic injuries, police said on Saturday.

The injuries ranged from minor to severe, but none appeared to be life-threatening, Wichita police Captain Aaron Moses said at a news conference. The two people killed were pronounced dead at the scene, he said.

Moses said a 34-year-old woman was driving the truck, which ended up in a field at the west end of the Stryker Sports Complex. She has been cooperating with investigators, he said, but when asked whether she had been arrested, he said only that she was in custody.

"We know what happened, but now we're working very hard to find out why it happened, and we're not there yet," Wichita police Chief Joe Sullivan said.

The injured were two youths aged 5, two aged 8, a 9-year-old and five adults, police said. In addition to those 10 people, one adult was hospitalised for non-traumatic medical issues.

The driver had a child playing football at the complex, but not on the field where the incident took place, Moses said. The truck involved had two juveniles as passengers, he said.

"Today is a heartbreaking day for Wichita," Mayor Lily Wu said.

"Families came to Stryker Sports Complex to enjoy a Saturday afternoon, watching their children play soccer and no one could have imagined the tragedy that would unfold."