A mother was left horrified after security camera footage from her back garden showed a stranger jump over her fence and sniff underwear hanging on a clothesline.

Oksana Panich, from Mandurah, Western Australia, was watching a film with her 11-year-old son at the time, oblivious to what was happening.

But after she noticed her pack of cigarettes missing the next morning, she decided to review video from her security camera, WA Today reported.

"It's the most disgusting thing I've seen," Panich said of the footage, which was dated Friday (5 May). She described the intruder as "psychopathic".

The suspect, wearing a baseball cap, can be seen entering the garden before making a beeline for some underwear hanging on the clothesline.

For about 30 seconds, the unknown male appears to sniff the underwear before walking in full view of the camera as he left the property.

"It was pretty scary because I never knew he was there," Panich said. "I don't have a man in the house and my son is 11, so you can (imagine) how safe you can feel in the house."

She said she reported the incident to police, who are investigating.

"I just want to find this pervert,"Oksana Panich told Storyful.

The mother also took to social media to warn others about the intruder, encouraging anyone who recognised the man to contact police.

"Please be aware there is a intruder sneaking around backyards," she wrote on a Mandurah Facebook page.

"He likes to sniff women's panties and steal cigarettes. If you recognise this creep please forward a name so he can be reported to police."

If you have any information about the incident call Mandurah police on 131 444 or contact Crime Stoppers on 1800 333 000. Alternatively, information can be reported online at crimestopperswa.com.au.