What happened at Tiananmen? In 60 seconds
4 June 2014 Last updated at 09:31 BST
Thousands of security personnel have been deployed in Beijing to prevent any commemoration of the crushing of the student-led protests in Tiananmen Square 25 years ago.
The protests were the biggest rally against Communist rule since the People's Republic was founded in 1949.
Hundreds of thousands called for democratic reforms in a peaceful demonstration largely focused on a gathering in Tiananmen Square.
After weeks of protests, the authorities responded on 3-4 June 1989.
Here's a look at what happened - in 60 seconds.
Video produced by Michael Hirst