Bank of China International is leading the deal, which could be the world's biggest AT1 offering.
The Chinese bank has recently hosted a global roadshow for the potential deal, sources said.
The US$6.5bn offering of preference shares could include a US$5bn tranche and a 1bn tranche, the sources said.
BOC could also issue in other currencies.
However, preference shares in US dollars and euros would allow the bank to attract more demand and attain better pricing than other currencies, they said.