China's ruling party has compiled a book based on a call by President Xi Jinping for art to serve communism, state media reported Monday, heightening concerns among free speech advocates over artistic restrictions.

Xi's speech last year, urging artists not to chase popularity with "vulgar" works but promote socialism instead, drew comparisons to a 1942 address by China's communist founding father Mao Zedong insisting that culture should have an appropriate political purpose.

"Art and culture will emit the greatest positive energy when the Marxist view of art and culture is firmly established and the people are their focus," read a transcript of the speech released by the official news agency Xinhua last week.

The text has now been edited, with some widely reported controversial elements removed, and previously unreported supposed passages added, including a list of more than 100 foreign cultural figures Xi found inspiring, among them Wagner, Tolstoy, Victor Hugo, Jean-Paul Sartre and Ernest Hemingway.

The book's chapter titles include "Strengthening and improving the Party’s leadership over artistic practice" and "The achievement of a great rejuvenation of the Chinese nation requires a prosperous flourishing of Chinese culture", state broadcaster CCTV reported.

The ruling party's publicity department issued a directive urging local authorities to organise seminars and classes to teach the book's contents, Xinhua reported.

Chinese authorities maintain a wide-ranging system of censorship that reaches deep into the media and online networks, and Hu Jia, one of China's most outspoken dissidents, said the renewed emphasis on Xi's text augured badly for free thinkers.

Xi was targeting the arts as a means of "undetectable control", he told AFP.

"The Communist Party is emphasising the importance of culture, but it's a socialist culture -- it is not a free culture of democracy and rule of law," he said. "What the Communist Party is promoting, it’s not culture or art -- it’s all propaganda."

Soft power is increasingly important to China as it attempts to expand its influence abroad, but campaigners say the process will be difficult without allowing creative freedoms.

Hu added: "As long as you come out with a voice that's different from theirs, it doesn't matter whether it's poetry, painting, movies, television, or any other artistic practice -- it's likely the political police and then the jails that will await you."