BEIJING - Beijing's Tiananmen Square was closed to the public on Wednesday for a government-organised coming-of-age ceremony for 18 year olds, an apparent attempt to thwart any student commemorations.

Wednesday marks the 86th anniversary of the May Fourth Movement of 1919, the first mass protest in modern Chinese history, and also of the beginning of the student democracy protests on May 4, 1989, and there had been speculation that protesters would gather in Beijing.

Tiananmen Square, imbued with historic symbolism as the centre of May Fourth and the Tiananmen Square Massacre, in which PLA troops and tanks killed hundreds, if not thousands of unarmed students, on the orders of the Chinese Communist Party, will be closed until 11:30 a.m. (0330 GMT), state radio said.

In Hong Kong, students are planning a commemoration of May 4th and have built a memorial to the Tiananmen Square Massacre.

Fresh demonstrations had been rumoured to be planned in Beijing and other cities for Wednesday. Police security was tight near the embassy and the ambassador's residence.

China has also clamped down on Web sites spreading calls for new protests, sent blanket messages to mobile phone users urging them not to participate in illegal protests and arrested dozens of suspected protest leaders.

The May Fourth Movement, named for the day major protest erupted in 1919 against the Versailles Treaty after World War One that handed German territorial concessions in China to Japan, is credited with giving birth to modern Chinese nationalism.