A former Chinese police chief rumoured to have tried to defect visited a US consulate, it was confirmed Thursday, fuelling a political intrigue analysts say may signal a power struggle in China.

The speculation about Wang Lijun, who has close links to a high-profile contender to join China's top decision-making body, comes at a crucial time with a once-in-a-decade leadership transition set to start later this year.

The US embassy in Beijing confirmed Wang's visit to the consulate in Chengdu but declined to comment on the rumours he had sought asylum, saying only that he had gone there for a meeting and left "of his own volition".

China's official Xinhua news agency said authorities were "investigating the incident in which Chongqing Vice Mayor Wang Lijun entered the US consulate in southwest China and remained there for one day".

Analysts said the confirmation of the visit would further fuel speculation surrounding Wang and his boss, Chongqing's colourful but controversial Communist Party secretary Bo Xilai.

They said it may hamper Bo's chances of promotion to the nine-member Politburo Standing Committee, China's top decision-making body, when seven members, including President Hu Jintao, step down later this year.

As Bo's deputy, Wang -- whose current whereabouts are unknown -- won a reputation for graft-busting with a campaign to rid the southwestern city of corruption in which dozens of officials were arrested.

But Chongqing authorities removed him as police chief last week before announcing Wednesday he was on leave, receiving "vacation-style treatment" for stress and over-work.

"Wang's dismissal is most likely the result of high-level in-fighting," Willy Lam, a leading China expert at the Chinese University of Hong Kong, told AFP.

"Bo's chances for the (Politburo appointment) have been adversely affected. It's long-standing 'organisational principle' of the CCP (Communist Party) that a region's No. 1 has to take political responsibility for the misdemeanours of his subordinates."

Sick leave is a term often used as a euphemism for a political purge in China's murky one-party communist system.

China's Vice Foreign Minister Cui Tiankai refused to comment Thursday on Wang's visit to the US consulate, only telling reporters the issue had been resolved "relatively smoothly".

The Chongqing government refused comment on the visit, which came ahead of a planned trip to the United States next week by Xi Jinping, China's vice president and likely successor to President Hu Jintao.

But there was feverish speculation about Wang's motives -- and his current whereabouts -- on China's popular microblogs.

The state-run Global Times newspaper said a government statement on Wang's illness was forwarded online 30,000 times within an hour of being posted, reflecting intense interest in the nation's high-level internal politics.

Even before state media reported Wang's visit to the consulate, the information was widely circulating on microblogs Thursday, a day after Internet censors blocked searches and content containing Wang's name.

Rumours that Wang was seeking political asylum appear to have been stoked by reports that scores of police vehicles descended on the consulate on Tuesday evening.

As Bo's right-hand man, Wang, 52, an ethnic Mongolian, gained national fame while toppling former city deputy police chief Wen Qiang in a massive crime crackdown. Wen was executed in 2010.

Known as a "princeling" due to his father's revolutionary legacy, Bo has encountered opposition from those who are against nepotism and hereditary rights in China's political system.

Bo's crackdown on corruption and organised crime in Chongqing was widely popular, although responses to his campaign to instill "red" or communist-style patriotism in the municipality were mixed.

On Thursday, the Chongqing Daily, the city's official newspaper, championed the crackdown on the mafia, saying nearly 97 percent of the city's residents said they "had a sense of safety" and "no longer feared going out".

"Bo is seen as a Machiavellian figure who is willing to risk anything to achieve his goals," Lam said.

"His high-profile campaign to sing red songs and crack down on triads are regarded as cynical ploys to boost his own political standing."