The strange disappearance from public view of China's presumptive new leader is turning a year that was supposed to showcase the Communist Party's stability into something of an annus horribilis.

Over the past week, the new leader, Xi Jinping, has missed at least three scheduled meetings with foreign dignitaries, including U.S. Secretary of State Hillary Clinton on Wednesday and the Prime Minister of Denmark on Monday. Speculation that his health, either physical or political, has prevented him from making public appearances is rife on the Chinese Internet, but there has been no official explanation for his absence.

While some people with ties to the party elite say they suspect that Mr. Xi's ailments are not serious, his unexplained absences are especially conspicuous on the eve of what is supposed to be China's once-in-a-decade transfer of power. It also adds to a litany of woes that have disrupted the Communist Party's hopes that a seamless political transition would send a signal of strength to the Chinese people and the world at large.

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Two unusual political scandals have sidelined people considered contenders for seats on the all-powerful Politburo Standing Committee, most recently including a close ally of President Hu Jintao's. China's economy has fallen into an unexpectedly deep slump, confounding government forecasts for a measured slowdown. Party leaders have also yet to announce a date for the 18th Party Congress, the event to mark the retirement of this generation of leaders and the accession of the next, though it is supposed to take place as soon as next month.

Mr. Xi was internally designated the presumptive heir to Mr. Hu as the leader of the Communist Party, head of state and chairman of the top military oversight body in 2007, a full five years before he was expected to assume those posts. Party bosses have tried to name future leaders well in advance to prevent destabilizing jockeying for power. Smooth transitions are considered by many Chinese as a crucial test of the Communist Party's longevity, and its leaders are eager to make the case that their authoritarian system can manage China better than a multiparty democracy could.

Analysts who follow Chinese politics say the transition is still likely to happen roughly along the planned lines. They also say that the core leadership team around Mr. Xi is slowly taking shape, with the lineup of the Standing Committee coming into focus as the congress draws near.

But at the very least, the atmospherics are turning out to be far messier than envisioned, with officials stumbling to maintain their usual careful choreography.

On Wednesday, after Mr. Xi did not meet Ms. Clinton and Prime Minister Lee Hsien Loong of Singapore, diplomats said privately that he had a bad back.

The situation then got odder. Foreign journalists had been invited to a photo opportunity between Mr. Xi and Prime Minister Helle Thorning-Schmidt of Denmark. On Monday, however, the Foreign Ministry denied that any such meeting had been scheduled and said other Chinese officials would meet the Danish leader.

While Chinese leaders often do not appear in public for long periods, cancelling meetings with foreign dignitaries at the last minute is highly unusual. Adding to the uncertainty is the lack of an official statement of any kind, with observers speculating about car crashes and heart attacks.

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"There's every sort of crazy rumour about Xi's health," said a senior Chinese journalist, who asked not to be identified due to the sensitivity surrounding the case. "But no one is saying anything."

Mr. Xi could appear publicly at any time and quash the speculation about his status. But for now rumours are replacing real information. Some have it that he hurt his back swimming or playing soccer.

One well-connected political analyst in Beijing said he was told by party officials that rumours of skulduggery are wrong. But he said he was told that Mr. Xi, who is 59, had suffered a mild heart attack.

Adding to the conspiracy theories, on Monday a popular microblogging site, Sina Weibo, banned searches for the term "back injury."

Almost as if to assuage worries about Mr. Xi's health, a newspaper on Monday ran a picture of him addressing students at the opening of the fall semester of the Central Party School. The photo and speech, however, were from Sept. 1, the last confirmed date of Mr. Xi's being seen in public.

New York Times News Service