Shanghai mayor Han Zheng at the crossroads

Han Zheng was 48 when first named mayor of Shanghai in 2003, the youngest person to hold the post in 50 years.

Unlike most political stars in the party's orbit, Han did not cut his teeth on a rotation through backwater postings followed by a stint at a second-tier city - he has spent his entire career in Shanghai. And that has proved both a blessing and curse.

Han is part of the Shanghai clique, drawing power and possibly protection from former leader Jiang Zemin .

But his lack of experience in roles elsewhere on the mainland limits his upward mobility, according to the party's own rules.

An interesting bet can be made on whether Han is allowed to sidestep that obstacle and is ushered into the Politburo at the party congress.

With Shanghai's current party chief Yu Zhengsheng strongly tipped to ascend to the Politburo Standing Committee, the chances are that if Han replaces Yu he would make it to the Politburo as well.

Han's tenure as Shanghai mayor has been punctuated by impressive successes - the city's hosting of the World Expo in 2010, its rise as the world's busiest container port that same year and the current strides it is making towards becoming the top renminbi trading, clearing and pricing centre by 2015.