There are two types of limited company in Hong Kong. Private and public. If a company has more than 50 shareholders, technically speaking, this is an "ordinary" public limited company.
If a public limited company is listed in Hong Kong Stock Exchange, we then call it a Listed Company with shares trading in Stock Exchange. Apart from the Companies Ordinance, this company has to compile with the Listing Requirements of Secuities Ordinance and Hong Kong Stock Exchange.