A "risk incident" at a Shanghai branch involved 768 million yuan (USD 122 million) and was related to its notes business, the bank said in a statement to the Hong Kong stock exchange.
Notes, also known as bills of exchange, are securities issued by financial institutions, often as short-term financing tools, and payable to the bearer.
Financial magazine Caixin said that the notes had been sold to the bank as part of a repurchase agreement.
A number of bank employees who handled the bills had turned themselves in to police, it added.
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The bank, which only listed in Hong Kong in late March, said in its statement on Friday that the incident happened "recently".
It is the third such case in China to come to light this year, and takes the total involved to 5.66 billion yuan.
Agricultural Bank of China, one of China's biggest banks, admitted in January that two of its employees stole notes worth 3.9 billion yuan to invest in China's stock market, which imploded in mid-2015.
The China Banking Regulatory Commission issued a notice last week requiring banks to improve their risk controls on commercial bills and check their authenticity, Bloomberg News reported, quoting people familiar with the matter.