"The firm's violation is very serious, so the inspectorate decided to exceed the maximum fine frame to discipline them," said Tu Luong, deputy director of HCMC's department of information and communications. 

"We will coordinate with the city department of tourism to strengthen inspection to avoid any recurrence of this unfortunate incident," Luong told VnExpress. 

Saigontourist Travel Service Company, a leading Vietnamese travel company, on the same day sanctioned its staff in charge of promotional publications and terminated its relationship with the Chinese company which supplied the brochures.

Its spokesperson said the firm acknowledged the seriousness of the issue and has instructed its staff to strictly review all of its promotional materials at all of its offices and branches.

One day before the company was fined, the 100-page brochure featuring Zhangjiajie’s landscape in central China was given to some visitors when they came to Saigontourist office on Le Thanh Ton Street, HCMC's District 1 and asked for information about the place.

On the brochure, a line says that it is compiled by "Zhangjiajie Foreign Affairs and Tourism Committee" and the last page features a picture of the nine-dash line which represents China’s fraudulent East Sea claims in flagrant violation of Vietnamese sovereignty over its waters.

The line claims 90 percent of the 3.5-million-square-kilometer East Sea, known internationally as the South China Sea, belongs to China. The claim has been dismissed by the international community. It clashes with claims by Brunei, Malaysia, the Philippines, and Taiwan, apart from violating Vietnam's sovereignty.

The brochures have been seized by the authorities.

Vietnam has to deal with several cases involving the nine-dash line recently. Last month, Chinese tourism brochures carrying the line were found in display by Chinese travel agency Hola China at the three-day International Travel Expo (ITE HCMC), promoting tours to Shanghai.

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. The Hanoi-based Binh Minh Software Service Co., Ltd. was the Vietnamese distributor.

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 Vietnam's central province of Khanh Hoa.