Two hours after the 29th National Book Expo opened in Xi'an's Qujiang International Exhibition Center on Saturday, 200 sets of two-volume thriller The Longest Day in Chang'an were sold out.

Facing constant queries about the book, publisher China South Booky, a subsidiary of China South Publishing& Media Group, rushed to have 500 more sets sent by air to Xi'an.

By 9 pm on its first day, the book expo in the capital of Shaanxi province had drawn more than 101,000 visitors and sold 104,700 copies, according to the organizers.

Readers, especially younger ones, were not deterred by the summer heat from seeking out favorite books and having a chance to see beloved writers, including China's first chief scientist of the lunar probe project, Ouyang Ziyuan, and veteran writer Jia Pingwa, a native of the province.

Ouyang brought speeches and a collection of the four-volume Chinese Children's Encyclopedia of Space to the expo.

The scientist has gained a considerable following by popularizing science through hundreds of lectures nationwide.

"There're no aliens or other 'things' as legends say on the dark side of the moon, where Chinese lunar probe Chang'e 4 is working," Ouyang said on Saturday during a Readers' Conference.

"China is willing to share what we found with the world and work for our shared future," he said.

About 1,200 publishing organizations have brought 200,000 titles and will present hundreds of book-related events and forums during the four-day expo, which continues through Tuesday.

As the book expo is one of the most important publishing and reading gatherings in the country, the organizers extended the venues to 66,000 square meters, and offer free admission and services until 9 pm each day.

This is the second time Xi'an has hosted the expo - the first was in 1998. Two other Red cities with strong revolutionary tradition, Yan'an and Tongchuan, have been sub-hosts.

"We see the expo as presenting a grand gift to the celebration of 70th anniversary of the founding of People's Republic of China, representing publishing industry and people related," said Liang Yanshun, deputy head of the Publicity Department of the Central Committee of the Communist Party of China.

"Here, in one of the Red bases where our great revolution started, we're expecting a quality development of publishing in the new era, and to cater to people's greater needs of spiritual life with high quality," Liang said.

Party-themed books are focal points, while children's books are drawing the most visitors.

The expo is presenting many new releases in science for young readers, and traditional culture and Chinese heroes from ancient times to present are also featured.

Tech-combined publishing and the convergence of multiple media with publishing were hot topics in a forum on Sunday.

"It's time for publishers to take proactive moves, instead of waiting passively," Liu Xiaokai, a senior publishing official, said at the forum.

Other expo highlights include the many writers and artists native to the province. Among them, Jia Pingwa, who usually keeps a low profile, spoke at the expo.

"I've been writing for more than 40 years. In between, I left my home township to settle down in Xi'an. Here I got a clearer view of my hometown. I frequently return to my hometown, where I've been observing and writing about the whole country, and the world," Jia said.

Xi'an being the starting point of the ancient Silk Road, the city invited 34 countries involved in the Belt and Road Initiative to showcase books at the expo.

Sinologist Giray Fidan of Turkey, once the other end of the Silk Road, brought his version of Sun Tzu: The Art of War translated from Chinese into Turkish.

Fidan said it has been reprinted in Turkey 14 times.

"It's a bestseller because more Turkish people are yearning to know more about China and its culture," he said.