Riot police advanced on Hong Kong democracy  protesters in the early hours of Monday, firing volleys of tear gas after launching a baton-charge in the worst unrest there since China took back control of the former British colony two decades ago.

Some protesters erected barricades to block security forces amid chaotic scenes still unfolding just hours before one of the world’s major financial centers was due to open for business. Many roads leading to the Central business district remained sealed off as thousands defied police calls to retreat.

Earlier, police baton-charged a crowd blocking a key road in the government district in defiance of official warnings that the demonstrations were illegal.

Several scuffles broke out between police in helmets, gas masks and riot gear, with demonstrators angered by the firing of tear gas, last used in Hong Kong in 2005.

“If today I don’t stand up, I will hate myself in future,” said taxi driver Edward Yeung, 55, as he swore at police on the frontline. “Even if I get a criminal record it will be a glorious one.”

White clouds of gas wafting between some of the world’s most valuable office towers and shopping malls underscored the struggle that China’s Communist Party faces in stamping its will on Hong Kong’s more than 7 million people.

China took back control of Hong Kong from Britain in 1997.

Eight years earlier, Beijing’s bloody crackdown on pro-democracy students in Tiananmen Square in 1989 had sent shockwaves through Hong Kong as people saw how far China’s rulers would go to maintain their grip on power.

Thousands of protesters were still milling around the main Hong Kong government building, ignoring messages from student and pro-democracy leaders to retreat for fear that the police might fire rubber bullets.

Australia and Italy issued travel warnings for Hong Kong, urging their citizens to avoid protest sites. Some financial firms in the business district advised staff to work from home or from another location.

The U.S. State Department said in a statement on Sunday that Washington supported Hong Kong’s well-established traditions and fundamental freedoms, such as peaceful assembly and expression.