HONG KONG — A rising Chinese politician who was abruptly removed from office this summer was publicly accused Thursday of trying to seize control of the Communist Party.

The accusation against the politician, Sun Zhengcai, was made by an economic official during a session of the Communist Party congress in Beijing, and gives the most specific detail to date of the charges against Mr. Sun.

Mr. Sun had previously been accused of “grave violations of discipline,” a vague phrase that can include corruption or disloyalty to the party. But the accusation that he had plotted a political overthrow represents a personalization of the allegations: Rather than attempting to undermine the party, he is accused of transgressions against China’s leader, Xi Jinping.

Liu Shiyu, chairman of the China Securities Regulatory Commission, grouped Mr. Sun with a handful of high-level officials who have been toppled in recent years. He called them “figures in important and high places who were both corrupted and contrived to usurp the leadership of the party and seize power.”