Police rushed to the hotel after receiving a report this morning that a man and a woman, both aged 42, were fighting.
The woman and a boy aged six were found dead at the scene while the man was arrested on suspicion of murder and taken to hospital, police said.
The suspect was believed to have consumed alcohol and appeared unconscious in the hotel suite with minor wounds to his hand and face, police assistant district commander Chan Tsz-Leung told an evening press conference.
The woman suffered multiple cuts and wounds to her neck and wounds were also found on the throat of the boy.
Police retrieved a five-inch-long knife at the scene, Chan said. The motive for the killings remained unclear, with the suspect still in hospital and unfit to talk to police.
A source with knowledge of the investigation told AFP that a friend of the suspect had warned authorities in South Korea he was potentially suicidal shortly before the incident.
The Ritz-Carlton is located on the top floors of Hong Kong's tallest skyscraper -- the International Commerce Centre -- and is famous for panoramic views of the city and its Victoria Harbour.
"Our thoughts are with the family of the guests involved at this very difficult time," a hotel spokesperson in Hong Kong told AFP, declining to comment further as an investigation was ongoing.
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