Police in the city of Show Low, Arizona, say they are investigating an incident in which multiple cyclists were struck by a truck during a cycling event.
In an update on Facebook, the police said the incident happened at 7.25am local time, before the suspect fled the scene.
They said officers attempted to stop the vehicle, before the suspect was shot.
The Arizona Department of Public Safety has been asked to carry out an investigation.
Six victims have been taken to hospital, of whom four are reported to be in a critical condition, while two are decribed as "critical but stable".
A number of others were also treated for what were described as "walk-in" injuries.
The suspect, a 35-year-old man, is also in a critical but stable condition.