China's ruling Communist Party says three of its top former officials rigged votes during earlier party congresses, in a move that sheds light on the fall of members of Xi Jinping's rival factions.

The senior figures were removed from office over the last few years as part of Xi's sweeping corruption crackdown, which some analysts have called a political purge.

An article published by Xinhua state news agency on Thursday alleges that the three men bribed party members to vote for certain candidates in 2007 and 2012, potentially threatening Xi's ascension to the party's top spot.

Ex-security tsar Zhou Yongkang and Ling Jihua ─ an aide to former President Hu Jintao ─ are both already in jail following convictions on counts of bribery, abuse of power and illegally obtaining or disclosing state secrets.

The third man, Sun Zhengcai, the recently disgraced party chief of the megalopolis Chongqing who was once a favourite for promotion to the party's ruling council, is currently under investigation.

Xinhua said the three officials' past abuse of the voting system prompted the party to abandon the system of voting in favour of a “consultative” mechanism for choosing leadership during this week's 19th congress.

The lengthy Xinhua article follows a twice-a-decade political meeting where Xi secured a second five-year term at the head of the party and became the most powerful Chinese leader in decades.

Xi's re-election was decided by “unanimous vote,” according to the party, but what that “voting” process really entails is murky.

“Some comrades (at the 17th and 18th congresses) did nothing beyond putting a tick on the ballot, leading to random voting and a distortion of public opinion,” Xinhua said.

“Such elections saw votes determined by 'guanxi' (connections) and personal favours.” The voting system was introduced in 2007 as a move toward an “internal democracy” within the party.

By moving away from votes, “the party is decreasing the overall transparency of the selection process, and increasing the likelihood of potential vote-tampering through intimidation or even outright coercion,” Patricia Thornton, a Chinese politics professor at Oxford University, told AFP.

The article suggests the new mechanism largely depended on Xi's preferences.

“From April to June, Xi personally talked to 57 senior leaders and retired leaders to seek their suggestions,” it said.