BEIJING (Reuters) - EU criticism of China’s rule over Hong Kong is unfounded, China’s Foreign Ministry said on Tuesday, after an EU report called the disappearance of five booksellers the most serious challenge to the “one country, two systems” principle since the city’s return to China.

A printout showing Lee Bo, specializing in publications critical of China, and four other colleagues who went missing, is displayed outside a bookstore at Causeway Bay shopping district in Hong Kong, China January 6, 2016. REUTERS/Bobby Yip

The disappearances of the five publishers who sold books critical of Chinese leaders had provoked concern that China was using shadowy tactics to erode the formula under which Hong Kong has been governed since its return to China from British rule in 1997.

One of the booksellers, Lee Bo, a British passport holder, disappeared in December and surfaced in China almost three months later. He has since returned to Hong Kong and said he had not been kidnapped by Chinese authorities as many suspected, but Britain had said he was removed under duress.

The one country, two systems principle was called into “serious doubt” by the case of the missing publishers, the annual EU report released on Monday said.

“The case raises serious concerns about respect for human rights and fundamental freedoms and about the application of PRC (China) criminal law to acts that are not punishable under Hong Kong law,” the report said.

It said the case could have an impact on Hong Kong’s standing as a global business center.

Foreign Ministry spokeswoman Hua Chunying said the EU should “stop interfering in Hong Kong affairs”.

“The EU report disregards the facts and makes unfounded criticism about Hong Kong affairs. We express our firm opposition to this,” Hua told reporters at a regular press briefing.

“The Chinese government’s determination to implement ‘one country, two systems’ is unwavering and will not change,” Hua said.

Chinese officials have repeatedly said they would never do anything illegal and that Hong Kong’s autonomy was fully respected.

Hong Kong authorities are still waiting for detailed explanations from China regarding the booksellers and how Lee was able to cross into China from Hong Kong without his travel documents, including a British passport.

The controversy has exacerbated social tensions between Hong Kong and China, fuelling a fledgling independence movement among pockets of the city’s increasingly restive youth including those who took part in the 79-day “Occupy Central” democracy street protests in late 2014.