A mentally ill Hongkonger has been sentenced to an indefinite period at a psychiatric hospital for killing his 50-year-old mother and hiding her body under the bed while under the delusion that she was a “monster lizard”.

The High Court on Monday accepted recommendations from two psychiatrists and imposed a hospital order on Wong Chun-kit on one count of preventing the lawful burial of a body and one count of manslaughter based on diminished responsibility.

Mr Justice Wilson Chan Ka-shun said the case was a “tragic one” and the defendant’s mental state was “substantially impaired”, leaving him unable to distinguish right from wrong.

He cited the psychiatric reports, both of which indicated that the defendant lacked awareness of his own mental health condition and was unsuitable for outpatient treatment, leading to the recommendation for detention in a psychiatric facility indefinitely.

Chan ordered Wong to receive treatment at the Siu Lam Psychiatric Centre in Tuen Mun until he was deemed no longer a danger to society, rejecting defence barrister David Boyton’s plea for a seven-year jail term.

Wong, 28, had pleaded guilty to manslaughter last month on grounds of diminished responsibility, after prosecutors acknowledged he had suffered a relapse of schizoaffective disorder which substantially reduced his culpability in what was originally classified as murder.

Chan said the sentencing was the “most appropriate” both for public protection and Wong’s welfare.