The Chinese embassy is investigating claims that a Chinese citizen’s passport was defaced by Vietnamese border staff earlier this week.

Ms Zhong, from Guangdong, had handed her passport to Vietnamese border staff after arriving at  Tan Son Nhat International Airport on July 23.

She was surprised to see a handwritten note when she got it back.

“The border staff kept my passport for around three minutes and after I got it back, I saw ‘Fuck you’ was scribbled on two pages where the nine-dash line is printed,” she said.

All Chinese passports issued after 2012 feature a map of China and the “nine-dash line”, an area of the South China Sea that China has claimed as its own, over the objections from numerous Southeast Asian countries.

The maps with the nine-dash line can be seen on page 8, 24 and 46 of every Chinese passport. The F-bombs were written on page 8 and 24 of Zhong’s passport.

The Chinese Consulate-General in Ho Chi Minh City issued a statement confirming that the Chinese embassy was currently dealing with the matter. The People’s Daily Online reported that the Vietnam Embassy in China declined to comment on the allegations.

Meanwhile, Chinese tourists are busy earning a bad reputation for poor behavior in Vietnam. A recent video showing Chinese tourists harassing a Vietnamese fruit seller has outraged people, while another video shows Chinese tourists swarming a fruit platter at a Vietnamese resort.

The Chinese passport gained visa-free access to 99 countries last summer, becoming the world’s 37th most convenient passport, immediately behind Honduras and overtaking the Russian Federation.