Organisers striving to inject new momentum into the movement told crowds to gather at the main protest camp opposite the city's government headquarters for commemorations starting with an 87-second silence at 0957 GMT.
At that time on September 28, riot police shot 87 volleys of tear gas at crowds of largely peaceful protesters who had taken over a highway near the city parliament.
That decision backfired, drawing tens of thousands of sympathisers onto the streets and kickstarting a movement that has become the most concerted challenge to Beijing since the bloody 1989 Tiananmen protests.
But the Chinese government shows no sign of backing down and protest leaders are unsure of how to achieve their goals.
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Occupy Central, one of the main protest groups, called on supporters to don the same protective masks and goggles they wore to defend themselves when the street rallies descended into chaotic confrontations.
The protests have been dubbed the "Umbrella Movement" following the creative ways demonstrators used to shelter themselves from the heat, torrential rain, pepper spray and police batons.
Hu Jia, a prominent Chinese dissident on the mainland currently under house arrest, said he would unfurl his own umbrella in solidarity with Hong Kong.
"I will participate in this event. In my home prison in Beijing," he told AFP.