Australian authorities have announced a Aus$1 million (US$700,000) reward for information that helps solve the murder of a young German tourist in a small country town in 2005.

Schoolteacher Simone Strobel was last seen at a caravan park in the small east coast city of Lismore after a night out with her boyfriend and friends in February of that year.

The 25-year-old's body was discovered under palm fronds at a nearby sports ground six days later.

No one has ever been charged over her death.

This week's reward comes on top of a 10,000 euro (US$12,000) offer announced by officials in Bavaria -- her home state -- in 2014.

Australian police this year credited an Aus$2 million reward with helping crack the 32-year-old cold case murder of American tourist Scott Johnson.

The New South Wales state government on Thursday said the money would be given to anyone providing information that led to the killer's arrest and conviction.

"For 15 years, police have been determined to uncover the truth of what happened to Simone," police minister David Elliott said.

"Both the Lismore community and her loved ones in Germany deserve answers."

Local detectives have been working with police and prosecutors in Wuerzburg, Bavaria, to piece together Strobel's final movements.

"We know the truth is out there, and we know there are people who are holding it back," Superintendent Scott Tanner said.

"We have continued to examine evidence and speak with witnesses over the past 15 years, but we need additional help from the public to finally determine what happened to Simone."