In the ancient history of China, when did northerners migrate to the south of the Yangtze River for the first time?

During the Wei, Jin, Southern and Northern Dynasties, the northern minority regimes suffered repeated wars and defeats, and people were displaced and fled in large numbers.

It set off the first large-scale migration tide in the ancient history of China, and more northerners moved south.

-People's Education Edition "History of China"