That raises a good question: the role of Marx and Marxism, and how the CCP adopted and changed Marxism in all this.
I found the following article on Wiki about 'Marxist Leninist atheism' where similar atrocities in the old Soviet Union are described, similar to what has been happening in China:
https://en.wikipedia.org/wiki/Marxist–Leninist_atheism
The Bolshevik government's anti-religion campaigns featured propaganda, anti-religious legislation, secular universal-education, anti-religious discrimination, political harassment, continual arrests and violence.[40]
Initially, the Bolsheviks expected that religion would wither away with the establishment of socialism, hence after the October Revolution they tolerated most religions, except for the Eastern Orthodox Church who supported Tsarist autocracy.
Yet by the late 1920s, when religion had not withered away, the Bolshevik government began anti-religion campaigns (1928–1941)[41] that persecuted "bishops, priests, and lay believers" of all Christian denominations and had them "arrested, shot, and sent to labour camps".[42]
In the east, Buddhist Lamaist priests "were rounded up in Mongolia, by the NKVD in concert with its local affiliate, executed on the spot or shipped off to the Soviet Union to be shot or die at hard labor in the mushrooming GULAG system" of labour camps
It would be fascinating to outline the philosophies behind these actions, and what contribution (if any) Marxist developments and atheism played in what has been happening.