Police in Greymouth are struggling with the mystery of the melting boysenberries.

Constables alerted to the activation of the burglar alarm at a safety equipment shop about 4am found someone had thrown 1kg of frozen boysenberries at the front window, smashing it.

The fruit, while defrosting, was still cold, police said, suggesting it had been taken out of the freezer shortly before the incident.

Police want to speak to anyone who observed the incident or might be missing some frozen boysenberries.

- Greymouth Star