Police have been in Kawerau today, excavating a site relating to a cold case.

Mona Blades disappeared in 1975 while hitch hiking from Hamilton to Hastings - with police work on the case ongoing.

Her body and belongings have never been located.

Bay of Plenty officers have completed exploratory excavation work at a residential property in Kawerau, following sonar readings.

Detective Inspector Mark Loper says results required further analysis of the area - however nothing of interest has been found.

He says historic cases are periodically reviewed to ascertain whether any new information has developed.

He explains it's impossible to discuss in detail, the nature of the tip off which led police to Kawerau.

Police are calling on anyone who may have information about the disappearance of Mona Blades, to come forward so they can put the case to rest.