Zhang Hongbo, secretary-general of the China Written Works Copyright Society, the only collective copyright management organization for written works in the country, said the giveaways showed a sloppy approach to copyright if approvals had not been sought from copyright holders to offer their titles for free.

"I think it's hardly successful marketing if it's based on sacrificing the interests of copyright holders."

Zhang said the promotions also raised doubts, and showed a lack of faith in the development of the country's e-publishing industry, especially from the so-called traditional publishers.

Although the value of China's e-publishing industry reached 133.7 billion yuan ($21.6 billion) in 2011, Zhang said the share of e-books is still smaller than that of digital games and digital advertisements.

"Content providers in the country are weaker than the platforms and channels," Zhang said. "I fear this new tide of free e-book selling will cause them to have even lower confidence in the e-publishing business.

"That will bring bigger harm to the industry as a whole."

However, Yan Feng, a Fudan University professor and columnist on IT products and e-readers, said the giveaways was a good marketing tool to draw customers into buying Dangdang's other e-book products.

Yan said he had chosen 50 e-books in the promotion without being charged, while some of his friends seized 100.

"E-books will be the focus and highlight of the book market," Yan said, adding that Dangdang is simply attempting to create a foothold in that sector, faced with stiff competition from companies such as Jingdong and Amazon.

But he added that if the giveaways lasted too long, it could have negative effect on the industry and its own business.

As a reader, he said it would be more effective if online booksellers stopped "the price hype" and focused instead on improving the e-reading experience by using better design and editing.

"There's no such thing as a free lunch. A lot of effort goes into the launch of just one book. Price wars can only eventually harm book creators and producers," Yan said.