On Saturday tens of thousands of people gathered in Hong Kong to mark the 16th anniversary of the Tiananmen Square massacre. On June 4, 1989 Chinese troops violently crushed student pro-democracy protests. Human rights groups say hundreds — if not thousands — of unarmed protesters were killed. Hundreds more were arrested and as many as 250 remain in prison. Outside of Hong Kong, there were no public commemorations of the anniversary in China. Dissidents and relatives of the Tiananmen victims were reportedly put under government surveillance and warned not to take part in memorials. Protesters in Hong Kong also called on the Chinese government to release journalist Ching Cheong — the chief China correspondent for the Straits Times newspaper. China has claimed the journalist has admitted to being a spy.