Police have been digging in the rear garden of a residential property in Tokoroa as part of a missing toddler case.
Jefferie Hill, aged 2, went missing on September 1968 and the following year a coroner concluded he had drowned in a creek.
A body has never been found.
A privately-funded sonar search located an area of anomaly in the garden which police decided needed further investigation.
Detective Sergeant Kevan Verry says police are always open to receiving new information and will always investigate.
Wednesday's operation involved excavating an area about 1.5 square metres and about 75 centimetres deep.