Xi has skipped meetings with a number of visiting leaders and senior officials over the past week, including US Secretary of State Hillary Clinton, because of what sources told Reuters was a possible injury to his back suffered while swimming.
But Chinese officials have refused to give any explanation for Xi's absence from the public stage, giving rise to bizarre speculation on the country's Internet rumour mill.
According to various theories being floated, the 59-year-old Xi has had a stroke or heart attack, was the target of an assassination attempt or was secreting himself, preparing for war.
Xi has not been seen in public since September 1 and the continued unwillingness of the government to impart any information on the health or whereabouts of the man who is essentially China's president-elect was beginning to cause unease overseas.
"Something serious must have happened, because they would have put him on national TV right away had there been no serious physical problem," said Minxin Pei, professor of government at Claremont McKenna College in California.
"I rule out political foul play, that he is in some kind of serious political trouble. It's simply unimaginable," Pei said. "He gave a speech on September 1, and that's after Beidaihe - if he were in political trouble, he wouldn't have given that speech."
Beidaihe is the seaside summer retreat of senior Communist Party leaders, who meet there every August to hammer out policies for the coming year. This year the talks were likely to have focused on the new party leadership to be unveiled at the party congress expected to be held in October.
The congress, held only once every 10 years, is China's most important political event, and the fact that its timing has not yet been announced has fuelled speculation about discord within the Communist Party.
Still, foreign businessmen attending the World Economic Forum meeting in the Chinese port city of Tianjin were not fazed.
"I haven't heard anything that would give me concerns at this point," said Rafael H. Saavedra, vice president of engineering at Right Scale, a cloud computing automation and management firm from Santa Barbara in the United States.
"There is a lot of speculation with very little information about what is really happening," he said. "So I think probably there is a good reason and there is nothing really strange."
TIGHT-LIPPED
Foreign Ministry spokesman Hong Lei, asked about Xi's health, would only say that he had no information. Asked if he could confirm if Xi was even alive, Hong said only, "I hope you can ask a serious question."
The ministry, for the most part the only government department that regularly takes question from foreign reporters, has repeatedly declined to comment on Xi's current status and whereabouts.
As China has grown into the world's second-largest economy, the country's corporate spokesmen and even government officials have become more open and PR-savvy in dealing with domestic and foreign media.
But such people "encounter strong resistance from the more conservative elements who still think that the general health of the top leaders is a state secret," said Joseph Cheng, professor of political science at City University of Hong Kong.
"They think that this kind of information may affect the leadership succession process or the party congress. They lack a sense of accountability to the domestic population and the international community," Cheng said.
"Of course, they are concerned that talking about these issues may anger top leaders who don't want their health being discussed."
