A manhunt is underway for a man horrified witnesses said masturbated in the middle of a suburban park wearing nothing but a hat.

The man was reported to police on January 13 by a resident who lives across from the Luketina Reserve, in Wembley Downs, Perth.

She told police she was sitting on her balcony at the time, about 10pm, and the man was alone.

A manhunt is underway for a man horrified witnesses said masturbated in the middle of a suburban park wearing nothing but a hat (stock)

She told police the man was only wearing a hat and was performing the sex act on himself.

'Scarborough Police attended and conducted a foot patrol of the park area, and a vehicle patrol of the broader area, however the man was not located,' a WA Police spokesman told Daily Mail Australia.

The man is described as aged between 20 and 30 years old with fair skin and a solid build.

Officers from the Scarborough Police Station are investigating the incident and have urged anyone with information to come forward.