Hong Kong was alone in deciding to break the worldwide embargo and sell Zhao Ziyang's memoirs, Prisoner of the State, before its scheduled release date on Tuesday, the book's translator said.
May 19 was chosen because it was on that day 20 years ago that Zhao made his final public appearance before the state placed him under house arrest. He would die 15 years later, in 2005.
Bao Pu said Hong Kong bookstores had a habit of breaking embargoes and being the first to put books on shelves.
The South China Morning Post and Ming Pao obtained the book from Dymocks, and Apple Daily bought a copy from a Page One outlet in Hong Kong.
The 160,000-character Chinese version of the memoirs will go on sale later this month. It is titled Journey of the Reforms.
'The Chinese version and the English one are slightly different,' Mr Bao said. 'The Chinese one is closer to the original work [by Zhao], while the English version focuses on the movement leading to the bloody June 4 crackdown.