This source said Guan's formal promotion to police chief was still being processed.

The Guangzhou-based News Express said Guan had been promoted to party chief of the municipality's Public Security Bureau as soon as Wang left his post.

Wang, 53, one of the city's seven deputy mayors and a close ally of city party boss Bo Xilai, was stripped of his duties as police chief and assigned a portfolio that includes education and the environment. But four days later, he visited the US consulate in Chengdu , Sichuan, where he spent a night before leaving the next day. The following morning he was flown to Beijing, where he is said to be receiving 'vacation-style treatment' for stress.

Although Wang and Guan were both born into Mongolian families and grew up in the country's northeast, they have different political backgrounds and styles.

Guan, 42, spent 15 years in the central committee of the Communist Youth League, the power base of President Hu Jintao . He left the league in 2009 after being promoted to deputy party head of the Jiangjin district in Chongqing.

Since Wang was brought by Bo to Chongqing to help steer his anti-corruption campaign in 2008, Guan's promotion is seen as a victory for the Youth League over Bo, whose father, Bo Yibo, was a contemporary of Deng Xiaoping, political analysts said.

'Wang's removal is a severe setback to Bo's political career,' political commentator Johnny Lau Yui-siu said. Chinese University political observer Ivan Choi Chi-keung said Bo had apparently been vying for a seat in the Politburo Standing Committee, but the departure of his one-time protege Wang, and the latter's replacement by Guan, meant Bo's chances of promotion were slim.

'Rumour has it that both Hu and Premier Wen Jiabao do not appreciate him, including his anti-corruption campaign along with his revival of left-wing political culture, because the two top leaders so far have not visited Chongqing,' Choi said. 'Guan's promotion indicates that Bo has lost his power and influence ahead of the Communist Party's 18th congress later this year, since the central government has started to intervene in the selection of personnel in Chongqing to prevent Bo making the city his own territory.'

Rumours were also rife in the mainland's lively internet chat rooms and microblog sites that Zhou Qiang , the party chief of Hunan province, who came from the same Youth League background of Guan, might replace Bo in Chongqing.

So far, there are few signs on the streets of Chongqing of the political drama gripping the nation.

By all appearances, it is a clean, vibrant and law-abiding city.

Visitors setting foot in the southwestern municipality for the first time could be forgiven for thinking they had arrived in a police state. Police vehicles patrol the roads incessantly. But many in this city of nearly 29 million will insist without a second thought that they live in the safest city on the mainland, thanks to Wang Lijun, who launched a full-scale assault on organised crime - which included sweeping reform of the police force - when he took charge in 2008.

'Two fellow drivers with my company were robbed and fatally stabbed separately in November 2007,' said a middle-aged taxi driver. 'But today I seldom see a scuffle on the street, not to mention murder, after Wang took over the force.'

Still, a barely perceptible sense of dread lingers. A local journalist, who did not want to be named, said the editor-in-chief of a local newspaper was summoned to the Public Security Bureau and rebuked last year for reporting a murder case without first seeking its opinion.