Three people suffered life-threatening injuries in a single-vehicle crash on Interstate 29 between the Canton and Worthing exits.
Shortly after 5:30 p.m. Sunday, officials say an SUV with a trailer went into the ditch just north of the Canton exit on I-29 but they aren't sure what caused the crash.
Six people were inside the SUV; three were airlifted to the hospital.
Northbound traffic was shut down for a short period of time. The South Dakota Highway Patrol is still investigating.