Xinhua, Li Tao/AP Photo

By Gloria Riviera (@gsriviera) and Karson Yiu (@karsonwhy) TIANJIN, China - No one outside the Chinese government knows for sure where Vice President Xi Jingping is these days. The presumed leader in waiting has not been seen in public for over a week.

As the mystery over his whereabouts deepens, the government has yet to offer an official explanation or even acknowledge Xi's absence. This week online searches for Xi Jingping have been blocked.

While it's not unusual for the Chinese government to remain mum on the private lives of its public figures, it is odd that such a high-ranking government official would simply disappear so close to China's once-in-a-decade transition of power. The new government is expected to be announced next month.

Xi, who is 59, made his last public appearance was at the Central Party School on Sept. 1 in Beijing. He looked to be in decent health, but a string of recently cancelled public appearances with visiting foreign dignitaries is fueling online speculation.

Last week, an appearance with Secretary of State Hillary Clinton was cancelled at the last minute. It was likely Mrs. Clinton's last trip to China in her current capacity, and the two have worked relatively closely together several times during her tenure. But the Foreign Ministry gave no explanation for his absence nor did it explain his failure to meet with Sinapore's Prime Minister Lee Hsien Loong the same day.

On Monday, the Danish Prime Minister Helle Thorning-Schmidt was in Beijing, but did not meet with Xi. She later said in an interview that a meeting with the president had never been on her schedule, although a media advisory circulated on Sept. 5 reportedly listed a photo opportunity with the two leaders.

Willy Lam, a Chinese scholar at the Chinese University of Hong Kong who told ABC News that he has spoken with more than one Chinese government official in Beijing, says that Xi was hospitalized after Sept. 1 for an undisclosed illness that left him with what officials describe to Lam as a "contortion" on his face. For this reason officials do not want him to appear in public.

Xi is making good progress and the mystery illness is not expected to affect his participation in the transition of power. Xi is not known, Lam says, to be in the best of health but the event is proving to be embarrassing for the Chinese government which still considers the health of its leaders to be a state secret.

The South China Morning Post reported today that an unnamed source told the Hong Kong-based newspaper that Xi had injured his back while swimming. A second source told the paper the same thing. A third source described Xi as "unwell," but that it was not serious.

That did not stop the netizen community from swapping speculation ranging from a car accident engineered by a political enemy to a soccer injury.

It is common practice for the government in China to maintain silence, even secrecy, when it comes to high ranking officials. This year has provided ample examples. In March, Premier Wen Jiabao gave Bo Xilai, the former Chonqing party chief whose wife was recently convicted of the murder of a British businessman, a public dressing down at the conclusion of the National People's Congress the likes of which shocked even long time China watchers. But, recently, when Ling Jihua, formerly a close ally of the current President Hu Jinato, was unceremoniously demoted there was no mention of why. Reports have circulated that his son was involved in a late night car crash in the company of half-dressed female companions, but there has been nothing in the way of an official report on the incident.

Today Foreign Ministry spokesman Hong Lei dismissed any suggestion that Xi is suffering from a serious ailment.

But Kenneth Lieberthal, of the Brookings Institution, told the Wall Street Journal, "Something is amiss - otherwise, they would have found an opportunity for him to be seen. But whether he hurt his back or there is some other problem is something that at this point there is no way to know with confidence."