Senior Sergeant Brian Benn said the truck driver parked his vehicle on Larnach Rd and got out to clear a blockage at the back of the truck about 9.15am.
The truck "took off down the road", rolling about 150m down Larnach Rd before going over a steep bank and ending up straddling a creek among thick bush, Snr Sgt Benn said.
Retrieving the truck was "very difficult" and the road was closed for the task, he said.
A crane could not be used because of overhead powerlines.
"It was very lucky that no-one was injured. It was a full rubbish truck so very heavy - about 11 tonnes," Snr Sgt Benn said.
Damage was restricted to the truck and its contents, he said.
Reilly's staff returned from the job just before 2pm.