Police searching for a man who filmed a woman under the toilet door of a Fitzroy bar have released CCTV footage of a man they want to speak to.

The 24-year-old woman was in a toilet cubicle at a bar in Brunswick Street when she noticed a mobile phone being held under the door with the camera facing her, detectives said.

The woman left the toilets and alerted staff members who investigated and found a man hiding inside one of the cubicles.

The man told bar staff he had mistaken the ladies' toilets for the men's toilets and was asked to leave, police said.

CCTV footage from the bar on January 21 has now been released by officers who want to speak to a man filmed there.

He is described as being Caucasian, aged in his 20s, about 191 centimetres tall, with short, brown hair, dark brown stubble and a European accent.

He was wearing a white cap, green T-shirt, black pants and thongs.

Anyone with information has been urged to call Crime Stoppers on 1800-333-000.