Hong Kong prosecutors on Tuesday filed a "seditious publications" charge against jailed media tycoon Jimmy Lai who already faces charges under a tough national security law that critics say has stifled freedoms in the Asian financial hub.

Lai, 74, the founder of the pro-democracy Apple Daily newspaper, appeared in court alongside six other former Apple Daily staff. The daily tabloid closed in June after authorities raided the newspaper, arrested staff on national security grounds and froze assets.

Lai already faces...