Authorities have shut down both directions of traffic on Interstate 90 between Humboldt and Montrose after a report of a crash involving a semi.
The crash occurred in the westbound lanes approximately one mile east of the Montrose exit shortly before 3 p.m., near mile marker 375.
Eastbound traffic has backed up for nearly one mile, reaching near-standstill conditions.
Authorities expect eastbound traffic to be closed only for a short period. No estimate was given for when westbound lanes might reopen.
Tony Mangan, public information officer for the South Dakota Department of Safety, said westbound traffic is being rerouted onto Highway 38 while crews are clearing the scene.
