BEIJING—Concerns over rampant corruption inside the ranks of the Communist Party emerged as a major theme of a critical Party Congress that began Thursday in Beijing, as President Hu Jintao and others cast notes of urgency over public contempt for widespread abuse of officials' powers.

Mr. Hu, in his last major speech as leader of the party, acknowledged rising public anger over abuses of power by China's ruling elite—an issue brought to the forefront in the public fall of former party star Bo Xilai this year.

Speaking Thursday morning in Beijing's Great Hall of the People, Mr. Hu acknowledged that corruption among Chinese officials is of major concern to Chinese people. "If we fail to handle this issue well it could prove fatal to the party" and the fall of the state, Mr. Hu said.