<span style="color: #222222;">Hong Kong riot police fired tear gas and water cannons at pro-democracy protesters hurling rocks and petrol bombs today tipping the violence-plagued city back into chaos after a brief lull in clashes.<br />''</span><br />'' <span style="color: #222222;">Tens of thousands of people defied authorities to march through the streets of the city in an unsanctioned rally, the latest expression of a popular revolt that has raged for the last 99 days.</span><br />'' <span style="color: #222222;"> </span><br />'' <span style="color: #222222;">But the rally descended into violence when small groups of hardcore activists tried to attack the city's main government complex. Police fired repeated volleys of tear gas and deployed water cannon trucks after Molotov cocktails and rocks were thrown over security barriers surrounding the complex, which has become a frequent flashpoint in the ongoing protests.</span><br />'' <br />'' <span style="color: #222222;">The clashes ended a relative lull in recent days in the intensity of skirmishes between police and protesters. </span><br />''  <br />