Two are dead and four others seriously injured after a pick-up truck reportedly hit pedestrians and other vehicles.
The multiple-vehicle collision happened on White Rose Way in Doncaster at around 11am on Sunday.
A black Mitsubishi L200 reportedly hit four pedestrians on the carriageway before colliding with a black Audi and silver BMW moving in the other direction, South Yorkshire Police said.
Two pedestrians died at the scene, and four other people were taken to hospital with serious but not life-threatening injuries, the force added.
Officers are working to identify the two victims and notify their next of kin.
Sign up for all of the latest stories
Start your day informed with Metro’s News Updates newsletter or get Breaking News alerts the moment it happens.
The driver of the Mitsubishi, a 30-year-old man, was arrested on suspicion of two counts of causing death by dangerous driving, two counts of causing serious injury by dangerous driving, and driving while unfit.
He has been bailed while police continue their investigation.
The force is appealing for witnesses and dashcam footage.
An air ambulance landed on the busy carriageway and shut down the surrounding road until midnight on Monday.