BBC-Chinese President Hu Jintao has opened a Communist Party congress that begins a once-in-a-decade power transfer with a stark warning on corruption.
Addressing more than 2,000 delegates, Mr Hu said that a failure to tackle the issue “could prove fatal to the party”.
China faced unprecedented opportunities and challenges, he said, and the nation should “aim higher and work harder”.
His speech kicks off a week-long meeting that will see a new set of leaders unveiled.
Security is very tight across Beijing, with many dissidents detained or under house arrest, rights groups say.
Mr Hu told delegates at the Great Hall of the People that China had to adapt to a changing domestic and global environment.
“We must aim higher and work harder and continue to pursue development in a scientific way, promote social harmony and improve the people’s lives,” he said.
China’s development should be made more balanced and sustainable, he said, and the “serious challenge” of corruption should be addressed.
“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,” he said.
Anyone who broke the law would be brought to justice, “whoever they are and whatever power or official positions they have”, he said.
The corruption warning echoed one delivered 10 years ago during the previous leadership transition, when the party was told it risked “heading for self-destruction” if it did not tackle the issue.
The months leading up to this congress have seen China’s political leadership rocked by a scandal involving Bo Xilai, the former Chongqing party leader once seen as a candidate for top office.
His wife has been jailed for murdering a British businessman and he is expected to face trial on corruption-related charges.
Across China, meanwhile, recent cases of official corruption have stoked public anger and there have been a series of high-profile mass protests focusing on land grabs and environmental issues.
On the internet, thousands of people have left comments appealing for better measures to fight corruption on official websites launched for the congress by the three major party mouthpieces – Xinhua news agency, People’s Daily and China Central Television (CCTV).
Economic growth has also slowed in recent months and the wealth gap is an issue of great concern, as is China’s ageing population.
Mr Hu said a new model for economic growth was needed to respond to domestic and global changes.