China's ruling Communist Party says a vice mayor of the financial hub of Shanghai is under investigation amid an ongoing drive against corruption at all levels of government.

The party's Central Commission for Discipline Inspection said on its website Tuesday that Ai Baojun was being probed on suspicion of "serious violations of discipline." The phrase almost always refers to graft.

Ai's name had already been removed from the list of Shanghai vice mayors, a likely sign that he will soon be fired and expelled from the party as a precursor to prosecution.

The 55-year-old Ai was appointed a vice mayor in 2007 and two years ago became director of the city's new Hong Kong-style free trade zone that has been heavily promoted by the central government.