Brochures are handed to a visitor at the International Travel Expo in Ho Chi Minh City in 2018. Photo courtesy of HCMC's Tourism Department.

They were displayed by Chinese travel agency Hola China at the three-day International Travel Expo (ITE HCMC), promoting tours to Shanghai.

The nine-dash line represents China’s fraudulent East Sea claims in flagrant violation of Vietnamese sovereignty over its waters.

It claims 90 percent of the 3.5-million-square-kilometer East Sea, known internationally as the South China Sea, which has been met with strong opposition from the international community. It clashes with claims by Brunei, Malaysia and the Philippines.

The brochures were spotted on the opening day of the expo and seized, HCMC authorities said on Wednesday.

"The nine-dash line was printed in a small map appearing at a corner of the brochure and one needs to look carefully to see it," Nguyen Minh Ly, head of the inspection team at the city's Tourism Department, said.

His team also shut down the Hola China stall.

"Though we discovered it in time and no brochures had been distributed to the public, it is still a lesson for the inspection team," he said.

ITE HCMC is an annual event that this year attracted over 250 customers and 39 publications from abroad who put up 300 stalls.

Vietnam has to deal with various cases involving the controversial nine-dash line recently.

Online game Onmyoji developed by Chinese firm NetEase has been banned in Vietnam after its latest update issued on Wednesday showed the nine-dash line, its Vietnamese distributor, Hanoi-based Binh Minh Software Service Co., Ltd, has said.

Binh Minh launched Onmyoji, a role-playing game, in Vietnam in January last year.

Vietnamese cinemas have stopped screening Dreamworks' animation movie "Abominable" after viewers spotted the nine-dash line in a scene.

Information about the movie, including its trailer, synopsis and show times have also been taken down by distributors on their homepage and the media.

In August e-commerce website Shopee Vietnam was told to get rid of a map showing the nine-dash line. It was printed in English and Chinese without a Vietnamese translation.

The infamous line had also caused an uproar in Vietnam in May when it was found on T-shirts worn by 14 Chinese tourists arriving at immigration at the Cam Ranh International Airport in the central province of Khanh Hoa.