The Commonwealth Bank has ruled out lending money to the proposed Carmichael mega coal mine in Queensland in a move green groups say adds pressure on the federal government to run out loans of its own.

A bank spokeswoman confirmed Australia's biggest lender would not be making loans to the Adani mine proposed for the Galilee Basin. The initial thermal coal mine requires about $4 billion, but later expansion could require as much as five times that investment.

Protestors wearing suits resembling Prime Minister Malcolm Turnbull and Adani chief, Gautam Adani, take part in a protest in Canberra on Thursday. Credit:Alex Ellinghausen

"Whilst in general we do not comment on specific clients, we can confirm that we are not amongst the banks who have been, or will be, asked to consider this financing," she said.

A spokesman for Indian-owned Adani said the miner "welcomes CBA's clarification and confirmation of their view", adding it was in line with the bank's stance earlier this year.