A police spokeswoman said officers were at the scene of a serious crash which had blocked the Luggate-Cromwell Road (State Highway 6) at Mount Pisa.
The crash involved a single motorcycle and happened shortly after 10.30am.
The motorbike had come to the attention of police earlier in the morning due to the manner of riding, and inquiries were under way to locate it when the report of the crash was made, the spokeswoman said.
"Sadly, the rider has passed away at the scene," the spokeswoman said.
The highway has been closed while the Serious Crash Unit investigates.
Two fire appliances and a support vehicle from Cromwell Volunteer Fire Station also attended the crash.
No other vehicles were involved.
Diversions are in place, via State Highways 8A and 8B.
Motorists have been advised to follow directions of emergency services or delay their journey.
A St John spokeswoman said a helicopter and a manager responded but were stood down prior to their arrival on scene.
"The ambulance attended the scene; however, was not required," the spokeswoman said.
