Investigators have been told the group were having a picnic in the gardens from early afternoon and stayed into the night.

The group were approached by a man armed with hammer just after midnight when he made demands for their property

The man waved the hammer towards the group when two other men attended the scene and stole the victim’s property before fleeing.

The three offenders got into a red ute and drove away.

A short time later, just after 2am, one of the victim’s credit cards was used at a convenience store on High Street in Thornbury.

Melbourne Embona detectives are investigating and have released an image of a man and a digital image of the same man that may be able to assist with their enquiries.

Detectives are keen to speak to any witnesses that may have been in the gardens at the time of the incident.

Anyone with information is urged to contact Crime Stoppers on 1800 333 000 or submit a confidential crime report to www.crimestoppersvic.com.au.