The protest that comes to mind is the Tiananmen square incident starting on April 17, 1989 and ending on June 4, 1989
Strange that in China it was called the June 4th incident and in the West it was the Tiananmen Square Massacre -- quite a difference in the way it was named.
Most of the protesters were students. The number participating which is at best a guess was 1.2 million people in the square itself. There were more cities about 400 cities in China alone that held protests.
The reported number of deaths on June 4th ranged from 180 to very nearly 10500.
If this is incorrect, you have to be just a bit clearer about what you want. There was a similar student protest in 1986. It was not nearly as large but it did serve to introduce the idea of something much bigger.