China's ruling Communist Party has launched a probe into its deputy Beijing chief, it said Wednesday, with reports calling her the most senior woman to fall in President Xi Jinping's anti-corruption drive.

Lu Xiwen, 60, is being investigated on suspicion of "serious disciplinary violations", the Communist Party's internal anti-graft body said on its website, using a phrase that normally refers to corruption.

Lu is also a vice mayor of the capital and an alternate member of the ruling party's Central Committee.

The announcement by the Central Commission for Discipline and Inspection came a day after it said it was probing Ai Baojun, a Shanghai vice mayor and a director of China's first free trade zone in the city.

The investigations come as part of a high-profile crackdown on graft by President Xi that has deposed several senior officials, notably former security chief Zhou Yongkang.

With corruption widespread in China, critics say the lack of transparency surrounding Xi's campaign means that graft investigations are used for political infighting.

Women are rare in the upper levels of Chinese politics, and state-run media said Lu was the highest ranking female official probed since Xi came to power.

Internal investigations into high-level party officials operate without judicial oversight. Once announced, they are likely to lead to a sacking followed by criminal prosecution and jail sentence.

The probe into Ai, 55, was seen as marking the entry of Xi's campaign into the Chinese commercial hub, a stronghold of his political rival and former president Jiang Zemin.