Cpl. Greg Church said the accident happened at about 6:50 p.m. AT at an intersection just off Highway 1 at Bayard Road in Wilmot.
"Four adults from the sleigh are being transported to hospital by ground ambulance with serious non-life threatening injuries," he said. "One adult from the sleigh is being transported to hospital via air ambulance with undetermined injuries."
The road was closed for several hours. Police said alcohol was not believed to be a factor in the crash.
The condition of the horse is not known.