Divya Gopalan:

This has been the scene every lunchtime since the week began, in an area considered to be Hong Kong's Wall Street.

Many office workers have joined the protest movement, which has gripped the city for nearly six months. And once they leave, riot police take over, clearing strategically placed bricks on the road, trying to get the commercial heart of the city back to business.

An uneasy calm on Friday caps off one of the most violent weeks since the protest movement began in June, prompting China's leader, Xi Jinping, to comment on the unrest for the first time, saying: "The continued radical violent criminal actions in Hong Kong have gravely trampled on rule of law and social order, seriously damaging the prosperity and stability of Hong Kong."

And he added the Chinese government strongly supports the Hong Kong police in enforcing the law. But anger against the police has been growing, with many accusing them of using excessive force against protesters.

Universities have become the new flash point, with intense confrontations between protesters and riot police, who fire tear gas, rubber bullets and water cannon, and protesters retaliating with stones and crudely made gasoline bombs.

At the Polytechnic University, the campus has been turned into a fortress.