A novel by an anonymous Chinese author living in America, which started life as a blog, has become a worldwide publishing sensation. It has been snapped up by publishers in 15 countries who have been impressed by the fact that it has sold more than a million copies in China and inspired a film by an Oscar-winning Chinese director. Some publishers even bought it before reading a translation. Yet none of the publishers, translators or editors knows the author's identity.

Under the Hawthorn Tree, a tragic love story set during the Cultural Revolution, is written under the pen name of Ai Mi. All that is known about the author is that she leads a reclusive life in Florida, having gone there to study. She is thought to be in her fifties or sixties, if only because her insight into the Cultural Revolution suggests someone who experienced first hand the political and social persecution of Mao Zedong's last decade. She tells her readers that it was inspired by a true story. Her central character – a young woman from a "politically questionable family" who falls in love with the son of a general – is based on a real person with names and places disguised.

In a publishing world where an author's identity is often more important than their talent, it is striking that publishers as far afield as Italy, Norway, Brazil and Israel have responded to the writing alone. Lennie Goodings of Virago bought it without knowing a word of Chinese – and was relieved to discover that it lived up to her expectations when she commissioned an English translation. She said: "It's a beautiful love story, almost like a Romeo and Juliet. It has that real simplicity about people trying to love each other across class. [Set] against the Cultural Revolution, it shows the startlingly intimate reach of politics in that period [which] even affects – and infects – their love."

Goodings asked someone from Shanghai who works in Virago's accounts department to read it: "Her face fell and she said, 'I'm not interested in the Cultural Revolution. It's my parents' generation.' The next day she was at my shoulder, eyes brimming, saying 'it's so wonderful and I cried'. On the basis of that, I bought it blind." Although the original blog was serialised on a website that was blocked by the Chinese authorities, an admirer had passed it to one of China's state-affiliated publishers, which has been overwhelmed by its sales.

Anna Holmwood, the English translator, said: "It doesn't present a problem for the Chinese government. If you were to take a particular political line about the Cultural Revolution, that might be problematic. But nowadays people are very open about talking about what a terrible time it was."

In the opening chapter of the book, which will be published by Virago this month, the central character is befriended by a Russian who teaches her a Russian song, The Hawthorn Tree. Ai Mi writes: "Of course, this had to be done in secret. Not only had everything associated with the Soviet Union become dangerous but, just as importantly, anything contaminated by the idea of 'love' was considered the bad influence and the putrid remains of the capitalist class. The Hawthorn Tree was deemed 'obscene', 'rotten and decayed', and of 'improper style' because the lyrics spoke of two young men … in love with the same young maiden."

The film version, directed by Zhang Yimou, the director of House of Flying Daggers, will be released in Britain at a later date.