Crime scene in 1972 Qld cold case

Police are digging up the backyard of a Mackay home after a tip off over the 1972 disappearance of Marilyn Wallman.

The 14-year-old vanished during a bike trip to school in the city's northern beaches in a chilling mystery that's baffled the north Queensland community and police for four decades.

About 10 minutes after she left home, her brothers followed the some route and found her bicycle and school port by the side of the road.

Crime Stoppers have received information in relation to the case.

"We're excavating at a residence there today," a police spokesman told AAP.

"We've declared a crime scene at a north Mackay residence and that's where we've got forensic officers there."