Friday marks the 32nd anniversary of China's deadly crackdown on pro-democracy protesters at Tiananmen Square in Beijing.
Police officers stationed around the square are questioning visitors and checking their bags on Friday morning.
The incident on June 4, 1989, resulted in a large number of casualties after Chinese troops fired on students and others demanding democracy in the country.
The Chinese Communist Party and the government are suppressing criticism of their handling of the incident, as the party prepares to mark the 100th anniversary of its founding in July.
The Chinese government maintains it made the right decision. Information on the incident is tightly controlled and speaking publicly about it is taboo.