The comments by Wang Qishan, who runs the party's anti-corruption watchdog, came after sources said a senior official who was considered a contender for promotion at autumn's key party congress is being investigated for "discipline violations".
Wang said the anti-graft inspections that have begun since President Xi Jinping took office five years ago routinely discovered the same problems.
"All of the issues discovered during the inspections reflect the weakening of party leadership, shortcomings in party building and insufficient efforts to strictly enforce party discipline," Wang wrote in the party's official People's Daily.
"Party concepts are faint, organisation is lax and discipline flabby. The root is in the party's internal political life being not serious and unhealthy," he said.
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As head of the Central Commission for Discipline Inspection (CCDI), Wang has been the chief enforcer of Xi's pervasive anti-corruption drive and is widely considered as the party's most powerful man after Xi.
Despite an unwritten retirement age rule suggesting he should step down at this autumn's party congress, Wang, who turns 69 this month, could be kept on by Xi as head of a new National Supervisory Commission that will combine the powers of several graft-fighting bodies, sources with ties to the leadership have told Reuters.
Wang said in his People's Daily piece the fight against corruption would remain "a long process".
Critics of Xi's anti-corruption campaign have long accused it of being an instrument to sideline political rivals.
"Poisonous Influence"
Sun Zhengcai, the Chongqing party boss abruptly removed from office on Saturday, had been seen as a potential candidate for elevation at the autumn congress and as a possible future premier, but his star had waned since coming under criticism from the anti-corruption watchdog.
The government has yet to say what has happened to Sun.
Sources with ties to the leadership and foreign diplomats say Sun has been out of favour after the CCDI criticized Chongqing authorities in February for not doing enough to root out lingering "poisonous" influence from a disgraced predecessor, Bo Xilai.
Bo was once himself a contender for top leadership before being jailed for life in 2013 in a dramatic corruption scandal.
Xi's crackdown on corruption has seen dozens of senior officials jailed, reaching right into the upper echelons of the party. Xi has warned, like others before him, that the problem is so serious it could affect the party's grip on power.
Wang agreed with that assessment in his article.
"The greatest challenge to our party ruling for a long time and ruling fully is effective supervision," he wrote.
Exposing problems shows the party's confidence in facing them, Wang said.
"Putting out there the problems that objectively exist shows a high level of self-confidence and staunch focus, winning over the faith, trust and confidence of the people in the party's centre," he wrote, referring to the party's top leadership.
The crackdown has not just been focused on issues like bribery and using public money to fund lavish lifestyles. It has also taken aim at those whose political loyalty is found lacking or who express doubt in public about party policies.
Wang said some party members practised "political nihilism", casting aside their beliefs, while others were guilty of "phoney politics", seeing the word of the leadership as nothing more than slogans.
The party has long said it alone can deal with corruption, dismissing any calls for an independent body separate from the party to tackle the issue.
