Over half of China's population is comprised of ethnic minorities. The Han is the most populous of the minorities and is therefore considered a majority. Historically, the other minorities were peoples and cultures absorbed into the Han culture by conquer or geographical migration. A well known example is that of the Mongol invasion and subsequent Yuan dynasty. So compelling were the culture and traditions of the Han people, to the invading armies of the Mongol hordes in China, that they were adopted and made their own.
A brief description as well as images of each of the 56 recognized minority nationalities can be found in Minority Nationalities.
A study of the demographics of China is in Population.
NOTE- Minority Nationalities contains several graphics and may take a while to download on some computers.