The M5 East tunnel was shut in both directions after the crash at Bexley North just after 11.30am.
Westbound lanes have reopened while the eastbound lanes remain closed.
A “large quantity of hazardous oil” has been spilled, with experts from Fire and Rescue NSW still working to contain it.
Environmental experts are also on the scene.
The crash damaged the fire sprinkler system and the tunnel’s wall.
“This crash has taken out the critical fire suppression system in the tunnel,” Superintendent Adam Dewberry from Fire and Rescue NSW said.
As a precaution, firefighters will position two fire trucks at the end of the tunnel in case of a fire, he said.
All citybound motorists have been urged to avoid the tunnel.
”It is looking like it will take some time for eastbound [traffic to reopen],” Dewberry said.
Crews are also working to remove the vehicle.
The driver was able to exit the crashed truck with only minor injuries.
Motorists can also consider exiting earlier at the King Georges Road off-ramp to detour along the D5.
