Media playback is unsupported on your device Media caption Footage from recent engagements shows Xi Jinping smiling and waving

Speculation has been mounting about the whereabouts of China's Vice-President Xi Jinping, who has not been seen for over a week.

He cancelled a meeting with the visiting Danish prime minister on Monday - his fourth missed appointment.

He also failed to attend an important Communist Party meeting on Friday.

Mr Xi is expected to be appointed China's president at a party congress next month that will see major changes in the top echelons of leadership.

However, no date has been set for the meeting, fuelling reports that power struggles in the leadership have yet to be resolved, says the BBC's Asia analyst Charles Scanlon.

'No information'

Journalists had been given several days' notice of Mr Xi's scheduled meeting with Denmark's Helle Thorning-Schmidt on Monday, but the planned talks were taken off the programme.

In a nation that is now a vital part of the global economy, integrated into global diplomacy, and whose citizens are wired up to the internet, the old-style secrecy surrounding the Communist Party and its leaders looks increasingly untenable

Last Wednesday, he abruptly called off a meeting with US Secretary of State Hillary Clinton. On a visit to Washington earlier this year Mr Xi was given a reception benefiting a head of state.

He has also missed appointments with Singapore's prime minister and a Russian official.

A spokesman for China's foreign ministry evaded questions about Mr Xi's absence at a briefing on Monday, according to reports, saying he had "no information" to provide.

"We have told everybody everything," Hong Lei said, when pressed.

In response, there has been an inevitable wave of rumours, our correspondent says, with explanations on news sites and Twitter ranging from Mr Xi's possible involvement in a car accident to a power struggle.

Earlier on when Mr Xi missed his meeting with Mrs Clinton, rumours circulated online that he had injured his back while playing sports - suggestions ranged from football to swimming and golf.

Yet another rumour said he may have suffered a mild heart attack.

Who is Xi Jinping? Currently China's vice-president

Tipped to take over the reins from President Hu Jintao

Age 59 , born in Beijing

, born in Son of Xi Zhongxun , a veteran revolutionary and one of communist China's first generation leaders

, a veteran revolutionary and one of communist China's first generation leaders Married to singer Peng Liyuan Profile: Xi Jinping

Attempts to search Mr Xi's name on Chinese micro-blogging sites are now blocked.

Mr Xi is predicted to take the helm from current Chinese President Hu Jintao at the party congress, expected to take place in the second half of October.

But the dates of the meeting have yet to be announced, prompting speculation that some of the seats on the nine-strong politburo Standing Committee remain unallocated.

There have also been suggestions that the number of seats may be reduced from the current nine to seven.

Beijing has been shaken in recent months by its biggest political scandal in years with the dismissal of a rising star, Bo Xilai, after his wife, Gu Kailai, was investigated for and later convicted of the murder of a British businessman.

Mr Xi may merely be suffering from a bad back, as some of the more mundane rumours suggest.

But the secretive nature of the leadership and the febrile atmosphere in Beijing mean there is growing uncertainty about the long-awaited change in leadership to a new generation, our analyst says.