UPDATE: The southbound lanes of the Coquihalla Highway were partially reopened on Friday afternoon after being closed to traffic earlier in the morning because of a flipped semi.
According to DriveBC, traffic at the scene near Box Canyon has been reduced to a single lane.
Earlier, the southbound lanes were closed from just north of Hope to just south of Merritt.
Motorists are being advised to watch for workers and to obey traffic personnel.
The incident is between Portia and Box Canyon, and an assessment is in progress.
An estimated time as to when the southbound lanes will reopen is not available.
Detours are available, via Highway 8 to Highway 1, and Highway 5A to Highway 3.
DriveBC says the closure stretches from two kilometres north of Hope to one km south of Merritt.
DriveBC says motorists can expect heavy delays and congestion.