CBA CEO Ian Narev said that increasing internet speeds and the rapid development of smartphone applications has led to a fragmentation of the financial services industry.
That has opened the door for new players to enter the market, such as in the payments industry, he said.
"We consider we have got very, very good competitors in the major banks, we have got very good competitors in the next tier banks," Mr Narev told the G100 Congress in Sydney on Tuesday.
"We worry every day about all those competitors, but we worry equally about the niche players, many of them well resourced, many of them international.
"The Apples, the Googles, the Samsungs, the PayPals, the credit card companies, who can pick particular slivers as a result of the application of technology into financial services and compete. We need to be prepared for that."
Mr Narev welcomed competition, but said that it was unclear how regulation of the financial services sector was going to adapt to the participation of so-called niche players.
"That's something which we will all need to watch quite carefully," Mr Narev said.
"We've also got to remember what the world went over the last four or five years and realise that there must continue to be minimum standards that apply to any institution, no matter what it calls itself, that is entrusted with accepting money from the public.
"That will be interesting to watch."