Citing the Public Order Ordinance, the bureau warned that offenders face up to five years in prison for attending or a year in jail for promoting it.
It said offenders may also face charges under social distancing rules after police banned the rally citing the Covid-19 pandemic.
The Tiananmen massacre occurred on June 4, 1989 ending months of student-led demonstrations in China.
“We are asking Hong Kong people to light a candle at 8 pm, wherever you are.
Hong Kong government officials had hedged over the past month when asked whether the vigil could go ahead.
Four of them including Joshua Wong were handed jail terms after pleading guilty in early May, while others are awaiting sentencing.
This aerial view shows people at the beach at Big Wave Bay in Hong Kong on May 23, 2021. »