they aren't immigrants, they were Vietnamese citizens since 19th century. they were born and raised in Vietnam, so it is actually racist of you to regard them as pure Chinese, and not Chinese-Vietnamese.
Vietnamese has immigrants going to China today, illegally, by jumping the border. They are purebred 100% Vietnamese born and raised in Vietnam.
chinese ethnic in native are living to day in Vietnam they went to Vietnam also illegally, by jumping the border or by boats. pls bring them back to their homeland.