When asked to explain why China's leader-in-waiting has not been seen in public for 11 days, foreign ministry spokesman Hong Lei responded yesterday by saying: "I hope you will raise more serious questions."
But for China, Xi Jinping's whereabouts is a serious matter. His apparent disappearance comes only weeks before the country's once-in-a-decade leadership transition, when the 59-year-old is expected to begin the drawn-out process of replacing the outgoing President, Hu Jintao.
Since his last public outing at a school on 1 September, Mr Xi has cancelled a string of meetings with dignitaries including US Secretary of State Hillary Clinton and the prime ministers of Singapore and Denmark. Yet it may be Mr Xi's reported failure to attend an internal meeting of China's Central Military Commission which proves most telling, at a time when a leader-in-waiting would usually be pulling out all the stops to secure power over the country's armed forces ahead of the transition.
Meanwhile, no official reason for Mr Xi's absence has been offered by China's secretive leadership and, as a result, the information vacuum has been filled with rampant speculation about his possible whereabouts. China's foreign ministry merely denied that Mr Xi's meeting with the Danish Prime Minister, Helle Thorning-Schmidt, had ever been scheduled in the first place. "We have told everybody everything," Mr Hong insisted.
As China's local media is controlled by the state, it is not permitted to print speculation about leadership matters, leading discussion to take place in online social networks. A system of online censorship controls nicknamed "The Great Firewall of China" attempts to restrict online conversation by preventing users from searching for sensitive terms – yesterday, searches for "Xi Jinping" were blocked on the popular microblogging website Weibo.
However, code words allow users to circumvent China's attempts to control online discussion. In the days that Mr Xi has been absent, some have spread the word that he has been laid low by an injury he sustained while playing football. Others have suggested he has been hurt in a car crash. Staff at Beijing's 301 Military Hospital refuted claims that Mr Xi was receiving treatment there. Yesterday, two sources told Reuters news agency that Mr Xi had merely injured his back while swimming, while another anonymous source insisted: "He's unwell, but it's not a big problem."
Commentator Willy Wo-Lap Lam, a professor at Hong Kong's Chinese University and former China editor of the South China Morning Post, believes Mr Xi has suffered a stroke.
"He became seriously ill after a stroke and is now receiving treatment at a hospital in Beijing… I've been hearing the same story from both people in Xi's family and the party leadership," he told Norway's Aftenposten newspaper.
China's rumour mill is comparable to that of the Soviet Union during the Cold War years. When President Yuri Andropov fell seriously ill due to diabetes, kidney and circulatory problems, the government told the people he had a "cold".
In July last year, speculation that China's retired leader Jiang Zemin had died forced the state's Xinhua news agency to issue a statement to insist he was alive. And in April, the official organ of the People's Liberation Army was forced to put out a message urging military personnel to ignore online gossip and prepare for the "ideological struggle" of the leadership transition.
The government's own version of some events may shed light on why some of its citizens are inclined to put stock in less-than-credible rumours. For example, when Mao Zedong's hand-picked heir apparent, Lin Biao, disappeared in 1971, many raised questions about reports that he had died in a mysterious plane crash.
Far-fetched conspiracy theories about Mr Xi have been plentiful in recent days, including one which suggests he has been injured in an assassination attempt launched by supporters of the fallen former Communist Party rising star Bo Xilai, whose wife Gu Kailai was recently convicted for the murder of British businessman Neil Heywood.
Steve Yui-Sang Tsang, director of the China Policy Institute at the University of Nottingham, believes the assassination attempt story is unlikely to be true, not least because security in Beijing would have been heightened in the aftermath of any attack. He argues that it is not Mr Xi's absence which poses a problem for China – but the lack of information about it.
"Falling ill or suffering from some sort of injury a month or longer before a scheduled succession is not that big a deal and certainly should not be a crisis," said Mr Tsang. "This is becoming a big deal because the lack of transparency and the low credibility of the Party in the public mind provides scope for rumour-mongering," he said. "Until Xi is well enough to appear in public, it will be hard for the Party to stop all rumours and speculations."
As the world's second-biggest economy plays down the absence of its future leader, and struggles to contain the feverish level of speculation, it may become increasingly difficult to project the image that all is well within the Party ahead of its leadership congress in October.
Xi Jinping CV
China's Vice-President Xi Jinping was born in Beijing in 1953, and is the son of the revolutionary Xi Zhongxun, one of the Communist Party's founding fathers. He is regarded as one of the Party's "princelings" and has held several key offices, including vice-chairman of the party's Central Military Commission, which controls the army. Mr Xi is tipped to succeed President Hu Jintao when he retires as head of the Communist Party at its congress, which is due to take place in October.
His wife, the singer Peng Liyuan, had – until fairly recently – been more famous than him. She has previously described him as frugal and down-to-earth. However, his extended family is believed to have business interests in companies with assets worth $376m.