Teenagers - and their teachers - are largely unaware that deep kissing is a crime before age 16, research has revealed.
Exposing a hole in adolescents' knowledge, a church study found students did not realise that fondling and passionate kissing can be classed as indecent assault.
"Indecent assault can include deep kissing, such as with love bites, and fondling … and unlawful sexual intercourse includes oral sex as well as vaginal intercourse," said criminologist Keswick Chuk Wing-hung, a director of the Youth Enhancement Scheme at the Evangelical Lutheran Church of Hong Kong.
"It doesn't matter if the acts are consensual. If teachers or parents suspect teenagers of engaging in such activities, they should report to the police."
The church studied 88 cases of youths cautioned by police for sexual offences.
Boys rather than girls are usually charged, often receiving an official police caution, which will not show up as a criminal record.
"But if it happens multiple times, they will be taken to court and will get a criminal record for a sex-related offence. This can really hinder their employment prospects," Chuk said.
Since 2009, sex-related offences among under-16s in the New Territories have increased 42 per cent, with crimes committed by those as young as 12 years old, the study said.
Angela, a 15-year-old Lai Chi Kok student, was shocked to hear of the laws. "Hong Kong is a conservative place, but I had no idea kissing could be a crime."
A senior high school teacher said: "I did not know sexual contact for teenagers under 16 was criminal."
Church sociologist Joe Ching Kin-cho said: "It might seem backward, but youngsters should not spend too much time together because this will increase the likelihood of unlawful sexual contact."