Regional cadres began using the term "core" for Xi last December, but it then disappeared
A communique issued by top party leaders after a four-day meeting in Beijing called on all its members to "closely unite around the CPC Central Committee with Comrade Xi Jinping as the core", Xinhua said.
The announcement followed a gathering of 400 top party leaders in Beijing for a meeting known as the Sixth Plenum to discuss changes to party structure and discipline.
Xi has sought to bend the party to his will since taking its helm in 2012, and has already taken control of more levers of power than any leader since Mao.
Regional cadres began using the term "core" for Xi last December, but it then disappeared, suggesting that the Chinese president had encountered resistance to his efforts to further consolidate his power.