Most nationalities do not need a visa. If you need a visa you will need to apply at a China embassy.
Visa are required for nationals from Afghanistan, Angola, Armenia, Azerbaijan, Bangladesh, Belarus, Burundi, Cambodia, Cameroon, Central Frican Republic, Congo Republic, Congo (DRC), Cote d'Ivoire, Cuba, Eritrea, Ethiopia, Gambia, Georgia, Ghana, Guinea-Bissau, Iran, Iraq, Korea (North), Kyrgystan, Laos, Lebanon, Liberia, Libya, Moldova, Myanmar, Nepal, Nicaragua, Nigeria, Pakistan, Palestine, Panama, Senegal, Sierra Leone, Solomon Islands, Somalia, South Sudan, Sri Lanka, Sudan, Syria, Tajikistan, Togo, Turkmenistan, Uzbekistan and Vietnam.
Visas for Hong Kong are handled by Chinese Embassies.
Visa requirements Hong Kong
Foreign consulates in Hong Kong