If you look at countries like Singapore, Thailand, or Malaysia, you will find large populations of Chinese people. When was there a mass exodus of Chinese or was it small amounts over time?
For centuries the Chinese have migrated out and served as an economic class in southeast Asian countries. Most major cities have, or had, large Chinese quartiers. To varying degrees, they controlled foreign trade, especially since the demand from China drove the market in the South China Sea.
The first two large waves came under the Ming dynasty. At first, in the 15th century, Chinese were encouraged to go abroad and form trade networks. They were still considered Chinese subjects, however. One of the biggest waves came when the Ming dynasty fell to the Qing. At the end of the 17th century, this dynastic collapse prompted large numbers of Chinese to flee southern China as refugees on ships. A large number settled in what is today southern Vietnam. Even today in Vietnam, the word for 'ship' (tàu) is synonymous with Chinese -- a người tàu (literally 'ship person') means someone of Chinese origin.
In the early 20th century, the Kuomintang loosens migration requirements and the WWII and the Chinese Civil War provided the impetus for large numbers of Chinese to flee, especially to Malaya and Singapore.