Lender BOC Hong Kong Holdings Ltd (2388.HK) is considering a sale of its $6 billion subsidiary Nanyang Commercial Bank (NCB) to stop cannibalising the China business of its parent, people familiar with the matter said.

BOC Hong Kong is a unit of Bank of China Ltd (3988.HK), the fourth-biggest lender by assets in the mainland, and a sale of NCB will help streamline the group's operations in the country, the people said.

At $6 billion, the sale would be Asia's No. 3 bank deal of all time, according to Thomson Reuters data, behind Australia's Westpac Banking Corp's (WBC.AX) $17.9 billion purchase of St George Bank and Bank of America Corp's (BAC.N) $7 billion purchase of a stake in China Construction Bank (601939.SS), both in 2008.

One potential buyer interested in NCB is China Cinda Asset Management Co Ltd (1359.HK), the nation's No. 2 bad debt manager that listed in Hong Kong in December 2013, the people said.

China Cinda has been keen to buy a bank, as unlike its biggest rival Huarong Asset Management, Cinda does not own a bank, one of the people said. Having a bank will help China Cinda to tap cheap sources of funds to buy soured loans.

"We don't comment on market speculation," a BOC Hong Kong spokeswoman said in an e-mailed statement. China Cinda did not reply to emails and phone calls seeking comment.

The sources declined to be identified as the discussions were confidential.