BEIJING (REUTERS)- Beijing's mayor Cai Qi has been appointed as party chief of the capital city of Beijing, the official Xinhua news agency reported on Saturday (May 27).

Cai is close to Chinese President Xi Jinping, sources with ties to the leadership have told Reuters, and is virtually assured of a seat in the decision-making Politburo during the 19th Party Congress in autumn.

The Politburo currently has 25 members but it is unclear whether the number of seats could be expanded, reduced or remain the same later this year.

Cai and Xi overlapped during their time in various government positions both in the eastern province of Zhejiang and the south-eastern province of Fujian.

This is the latest move by Xi to put his allies in key positions ahead of the autumn party congress in Beijing.

In the past, politicians served as provincial governor or city mayor for five years before being promoted to party secretary of the province or city.

The party secretary outranks the governor or mayor.

Cai has been promoted quickly, as he only became the acting mayor of Beijing in October last year and the mayor in January this year.

Prior to becoming the acting Beijing mayor, Cai was a senior official at China's National Security Commission.