The truck has been recovered from Macquarie Pass.
According to the transport management centre, traffic crews will re-open the road in the next 10 to 15 minutes.
The Illawarra Highway is closed in both directions on Macquarie Pass due to a truck crash.
Motorists in light vehicles can use Jamberoo Mountain Road as an alternative route.
This diversion is not suitable for heavy vehicles which will need to use Picton Road instead.
Motorists are advised to exercise caution and allow extra travel time.
Emergency services and traffic crews are on site.