Bosses of China's postal bank and a regional city lender are among the latest financial bigwigs caught up in spreading corruption investigations.

Postal Savings Bank Gov. Tao Liming is "assisting an investigation by relevant authorities into a personal 'economic problem'," the bank said in an announcement Monday, using the usual euphemism in China for graft allegations.

The announcement on website of China's sixth-largest bank said another official, Chen Hongping, was also assisting investigations.

The notice gave no details, and Postal Savings Bank staff said officials responsible for answering media inquiries were not available.

Separately, the financial magazine Caixin and other reports said Zhuang Yonghui, former chairman of Yantai Bank, was being questioned in a corruption case that has led to detentions of more than a dozen people.

Calls to Yantai Bank's deputy general manager and marketing department director rang unanswered.

Yantai Bank is due to hold an extraordinary general meeting in late June. Among the items on its agenda is approval of the dismissals from its board of Zhuang and another bank official, and the resignation of a third.

The bank's former president, Liu Weining, was detained in eastern China's Zhejiang province in early February on suspicion he embezzled bank funds, the newspaper Global Times reported.

Hong Kong's Hang Seng Bank is the largest shareholder in Yantai Bank, with a 20 percent stake.

In one of the highest profile bank corruption cases now under investigation, a vice president at the Agricultural Bank of China, Yang Kun, was detained late last month.

Authorities are investigating allegations the lender provided loans to a property developer to help him cover 3 billion yuan ($476 million) in gambling debts in the casino enclave of Macau, Caixin said.

The Agriculture Bank said in a statement last week that Yang was assisting "relevant authorities" in an investigation but that it had no bearing on its own business.

The Postal Savings Bank, which mainly serves rural Chinese and smaller companies, was set up in 1986 and is wholly owned by China's mail system, the China Post Group. China's sixth largest bank in terms of assets, it is due to be restructured in preparation for a possible share listing.