Monaro Hwy was closed in both directions north of Bombala about 11am on Wednesday.
Live Traffic NSW said the closure was near High Lake Rd and was due to a truck crash.
Emergency services are attending. Live Traffic advised motorists to use an alternative route.
The diversions are:
- Light vehicles: Black Lake Rd and Cathcart Rd in both directions.
- Heavy vehicles: Park and wait in both directions.