A once-in-a-decade transfer of power is under way in China, the world's second-largest economy.
More than 2,000 delegates have gathered for a week-long meeting of the governing Communist Party, which will see President Hu Jintao give up his role as party chief.
Opening the congress with a "state of the nation" address, Mr Hu warned that corruption threatens the Communist Party and the state.
He said the party must stay in charge as it battles growing social unrest.
Mr Hu also promised political reform, but offered no dramatic changes and ruled out copying a Western style of government.
He acknowledged growing public anger over graft and issues such as environmental degradation, which undermined the party's support and led to surging numbers of protests.
"Combating corruption and promoting political integrity, which is a major political issue of great concern to the people, is a clear-cut and long-term political commitment of the party," he said.
"If we fail to handle this issue well, it could prove fatal to the party, and even cause the collapse of the party and the fall of the state. We must thus make unremitting efforts to combat corruption," Mr Hu said in a nearly two-hour speech.
The run-up to the carefully choreographed meeting, at which Mr Hu will hand over his post as party chief to anointed successor Vice President Xi Jinping, has been overshadowed by a corruption scandal involving one-time high-flying politician Bo Xilai.
The party has accused him of taking bribes and abusing his power to cover up his wife's murder of a British businessman in the southwestern city of Chongqing, which he used to run.
While Mr Hu did not name Mr Bo - a man once considered a contender for top office - he left little doubt about the target of his comments.
"All those who violate party discipline and state laws, whoever they are and whatever power or official positions they have, must be brought to justice without mercy," Mr Hu told delegates, one of whom was his predecessor, Jiang Zemin.
"Leading officials, especially high-ranking officials, must ... exercise strict self-discipline and strengthen education and supervision over their families and their staff; and they should never seek any privilege."
Handover of power
The congress ends on 14 November, when the party's new Standing Committee, at the apex of power, will be unveiled.
Only Mr Xi and his deputy Li Keqiang are certain to be on what is likely to be a seven-member committee, and about eight other candidates are vying for the other places.
The congress also rubber-stamps the selection of about two dozen people to the party's Politburo, and approves scores of other appointments, including provincial chiefs and heads of some state-owned enterprises.
"We must uphold the leadership of the party," Mr Hu said.
He also named health care, housing, the environment, food and drug safety, and public security as areas where problems had "increased markedly".
The meeting is a chance for Mr Hu to cement his legacy before retirement and ensure a smooth handover of power, and his prime-time speech was a chance to push his achievements and perhaps help steer a course going forward.
While he promised unspecified "reforms to the political structure" and more encouragement of debate within the party, he gave no hint that China would allow broader popular participation.
While Mr Hu will step down as party leader, Mr Xi will only take over state duties at the annual meeting of parliament in March.
Security was especially tight around the Great Hall and Tiananmen Square next door, the scene of pro-democracy protests in 1989 that were crushed by the military.
Police dragged away a screaming protester as the Chinese national flag was raised at dawn.
Chinese growth slowed for a seventh straight quarter in July-September, missing the government's target for the first time since the depths of the global financial crisis, but other data points to a mild year-end rebound.
Advocates of reform are pressing Mr Xi to cut back the privileges of state-owned firms, make it easier for rural migrants to settle permanently in cities, fix a fiscal system that encourages local governments to live off land expropriations and, above all, tether the powers of a state that they say risk suffocating growth and fanning discontent.