To my knowledge, he was the first to go to China and soon after denounce Mao’s regime in [private] letters that also related the gloomy everyday life of the people living there.
Raoul Vaneigem, Self-Portraits and Caricatures of the Situationist International
His letters reported on the stifling puritanism of everyday life in China. 
Raoul Vaneigem, Self-Portraits and Caricatures of the Situationist International
We will never sufficiently emphasize the importance of his letters in the denunciation of Maoism.
Raoul Vaneigem, Self-Portraits and Caricatures of the Situationist International