The suspect was spotted by the victim's friend on Tuesday night when they were on bus 296C from Kwun Tong to Tin Shui Wai.

After receiving the report, officers were dispatched to the bus station at Ju Ching Chu Secondary School and arrested the suspect, surnamed Chow, for outraging public decency. It is understood the man is a computer technician and that he doesn't know the victim.

Police also confiscated his rucksack, phone, clothing and Octopus card.

An identification parade will be conducted, police said, adding that they are also investigating whether there are other victims.

Police identified the suspect through a video which surfaced online days ago, showing him being caught red-handed taking upskirt pictures of the woman while they were queuing at a bus station at Tin Chung Court on August 31.

In the 22-second video, the white-haired suspect, who was wearing a long-sleeved shirt and trousers, was seen taking the pictures from a mobile phone hidden inside his rucksack, with the rucksack held below the woman's skirt.

The woman who filmed the entire ordeal told the victim about the incident just as the man lowered his rucksack beneath the victim's skirt. The man then immediately fled the scene.

The victim also posted about the incident on social media. "Two months ago, this man had been appearing at the bus station every morning I went to work and kept queuing up behind me every single time, but I never saw what he did," she wrote. She said she had simply thought it to be a strange coincidence.

The victim reminded other women to be careful, and said she has been contacted by others stating that they were also secretly filmed by a white-haired man.

According to another netizen, the man was a "serial upskirter" who she suspects to have taken upskirt pictures of her two to three years ago in the area. She also said the man works in Kowloon Bay.

The offence of "outraging public decency" under the common law is punishable with up to seven years of imprisonment.