Lui Lai-yiu is the first high-profile woman in socially conservative Hong Kong to tell of abuse as part of the #MeToo movement exposing sexual misconduct.

In an open letter posted on Facebook on her 23rd birthday, Lui did not name the man who abused her as a young teenager, calling him "coach Y".

Lam, the city's first female chief executive, told reporters she was "very upset" to learn about the abuse.

"The police chief will certainly follow up in earnest," she said, urging other victims to come forward "as difficult this experience is" so that allegations could be investigated.

The #MeToo campaign spread rapidly in October after multiple accusations against Hollywood movie mogul Harvey Weinstein and has since shaken artistic, media and political circles globally.

Lui's post included a photo of her holding a sign that read "#METOO" with her initials "LLY" and her eyes cropped out of the shot.

She recalled how she thought nothing of it when the coach offered her a massage at his home to relax her muscles, but that he then removed her clothes and molested her.

"In my mind he was a coach I respected," Lui wrote. "I had never thought he would do despicable things to his students."