China's likely next leader has called for greater unity in the ruling Communist Party in a speech published Friday -- a day after the biggest political drama to hit the country in years.

The speech, in which Vice-President Xi Jinping also said the party's authority had been weakened by a "lack of principles" among some members, was made before senior leader Bo Xilai was sacked as Chongqing party secretary.

But analysts said the decision to publish it on Friday in the party magazine Qiushi, or Seeking Truth, was a sign that China's leaders were keen to prevent potentially damaging infighting in the party.

Xi is expected to take over from Hu Jintao at the helm of the Communist Party later this year before becoming China's president in 2013 in a generational handover of power.

"To maintain the party's ideological purity is to guarantee the unity of the party," said Xi, accusing some members of "a lack or principles and corrupt behaviour which is not conducive to the purity of the party".

"Today some people join the party not because they believe in Marxism and want to devote themselves to Socialism with Chinese characteristics... but because becoming a member brings them personal benefits," he added.

"If the thoughts of members and cadres of the party are not pure, their ideas cannot be firm, and their political positions can easily change."

Xi did not mention Bo by name in his speech, delivered to cadets at the Central Party School -- a training ground for future leaders -- on March 1.

But David Goodman, an expert on Chinese politics, said it sent a message that party leaders did not want the kind of open politics that the charismatic and populist Bo was seen as practising.

"What happened under Mao (Zedong) was that individual whim rather party organisation came to rule," said Goodman, professor of Chinese politics at the University of Sydney.

"The Cultural Revolution smacks to many people of a lawlessness and the whims of a single ruler. How does that relate to Bo? He laid himself open to the criticism by going for an open, charismatic (style of) politics."

China announced on Thursday that Bo, a rising star once tipped to reach the very top in the ruling party, had been removed from his post in the southwestern metropolis of Chongqing.

He remains a member of the party's powerful Politburo, but analysts say his political hopes are finished after a scandal involving a key aide who was said to have tried to defect to the United States.