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Senior Sergeant Craig Dinnissen, of Dunedin, said police were urging people to get in touch if they saw suspicious activity in the area, and to take a photo if possible.
The incident is the latest in a spate of reports of naked men performing lewd acts at St Clair and St Kilda beaches in the past few months.
This man did not match the descriptions of earlier men who reportedly performed lewd acts in the dunes, bushes or on the beach.
Snr Sgt Dinnissen said the man was described as Maori, tall and of solid build, with black curly hair and facial hair, and nude.
He ran off into the bushes near Kettle Park before officers arrived.
"Once again it's concerning behaviour that we've got this stuff happening on our beaches in Dunedin.''
Officers continued to undertake preventative patrols in the area, Snr Sgt Dinnissen said.
"Once again, if people see anybody acting suspiciously, ring us.
"If you can get a photo, get a photo."