Twenty four years after the bloody crackdown on pro-democracy protesters in Beijing's Tiananmen Square, there is heavy censorship of references to the so called "June 4th incident" on China's most popular social media website.

The word "today" is just one of many in a long list of search terms that have been censored on Sina Weibo, reports the British newspaper The Guardian. Others include "tomorrow," "that year," "special day," and several combinations of numbers that could refer to June 4, 1989, such as 6-4, 64, 63+1 and 65-1.

But internet users are finding new ways to get around the censorship using references that can escape automatic detection.

Many of their posts noting today's 24th anniversary of the protests have been embedded in pictures, such as the iconic "tank man" photo with its tanks photoshopped into four giant rubber ducks, a reference to a well-known art installation currently floating in Hong Kong's Victoria Harbour.

Many prominent intellectuals and celebrities have reportedly taken the day off from posting on Sina Weibo in an act of quiet protest. One is the film-maker Jia Zhanke, who on Monday wrote, "Don't worry about forgetfulness — at least the Sina censors remember," according to the blog Tea Leaf Nation. The post has since been deleted.