Hong Kong police fired tear gas and water cannon Saturday as thousands of pro-democracy protesters hit the streets, defying authorities with another unsanctioned march after Beijing vowed to tighten its control over the unrest-plagued city.Crowds of black-clad protesters, many wearing face masks despite a recent ban, filled Causeway Bay, a popular shopping district, and clashes soon erupted as riot police tried to scatter them.Sustained volleys of tear gas were fired throughout the afternoon on the main island while a water cannon truck chased groups of activists as they blocked roads, built barricades and vandalised some businesses -- including smashing the windows of China's state-run Xinhua news agency office.Among those caught up in the tear gas clouds were rugby fans who had gathered in bars in Wanchai district to watch the World Cup final.Police were seen making multiple arrests throughout the day.The latest clashes came after China warned on Friday that it would not tolerate any challenge to Hong Kong's governing system and planned to boost patriotic education in the city, which has seen 22 consecutive weekends of youth-led protests.Hong Kong has been upended by the huge, often violent, pro-democracy protests which have battered the financial hub's reputation for stability and helped plunge the city into recession.Beijing has shown no willingness to meet protester demands for greater democratic freedoms and police accountability -- and activists show no sign of leaving the streets."The government and the police have been ignoring and suppressing the people's demands so we need to continue the movement to show them we still want what we are asking for," 18-year-old protester Gordon Tsoi, who was not wearing a mask, told AFP as he marched. "The entire government is being controlled by the central government now, so we have to come out to protect the freedoms we deserve," added another 17-year-old protester who declined to give his name.Police gave permission for an evening rally in the city's commercial district but rejected an application to march through the streets in the afternoon, citing safety fears given the months of clashes.As has happened so often in the past, protesters simply defied the ban and began massing in large numbers despite the risk of arrest and jail for taking part in an illegal assembly.Police later cancelled the evening rallies but crowds had already begun gathering, setting the stage for more unrest into the evening.Loathed by BeijingAmong those calling for people to come out on Saturday was Joshua Wong, one of the city's most prominent activists who was barred earlier this week from standing in upcoming local elections."Exercising freedom of assembly has become increasingly difficult as police in HK holds tighter grip in recent months. Yet we're not giving up our constitutional rights," he wrote on Twitter.Wong is loathed by Beijing with state media often branding him a "separatist" and a "traitor" because he campaigns for greater autonomy for Hong Kong.He denies seeking independence and says he simply campaigns for the democratic freedoms and autonomy Beijing promised Hong Kong for 50 years after the 1997 handover by Britain.Other people who advocate greater autonomy have been allowed to stand in the elections later this month.Beijing runs Hong Kong under a "one country, two systems" model that grants the city freedoms unheard of on the authoritarian mainland.But many activists fear those freedoms are being eroded by a resurgent Beijing, particularly since President Xi Jinping came to power.This summer's protests in which millions marched were sparked by a now-abandoned attempt to allow extraditions to the authoritarian mainland.But as Beijing took a hardline the movement snowballed.Protesters are demanding an inquiry into the police, an amnesty for those arrested and fully free elections.Over the months protests have got increasingly violent, with smaller groups of hardcore activists throwing petrol bombs and bricks as well as vandalising pro-China businesses.Police have responded with ever-increasing arrests, tear gas and rubber bullet volleys while crowd beatings of people on both sides of the ideological divide have become commonplace.