Standard and Poor's has cut the credit rating of some of Australia's major lenders, including the big four banks and investment bank Macquarie Group Ltd.


The changes are part of a shift in assessment criteria at the ratings agency, which saw it cut the ratings of 37 US banks earlier in the week.

ANZ Banking Group Ltd, Commonwealth Bank of Australia Ltd, National Australia Bank Ltd and Westpac Banking Corp Ltd have all had their credit ratings downgraded from AA to AA-.

Macquarie Bank's A long term rating has been affirmed, while Macquarie Group was cut by two-notches, from A- to BBB+.

The new approach takes into account offshore financing levels and Australia's high level of foreign debt.

S&P said Macquarie's bigger reduction reflected that "many markets in which Macquarie operates are inherently complex and volatile."

"This has a constraining effect on our view of Macquarie's business stability, and in turn our overall view of its business position," the agency said.

However, the S&P noted that Macquarie's position was adequate and its operations were diversified to its relative size.

On Wednesday, S&P downgraded the ratings of some of the world's biggest banks, including Citigroup, Goldman Sachs, JPMorgan Chase and Morgan Stanley.

The agency indicated in February that the banks may have their ratings downgraded as a result of the review.

Commonwealth group treasurer Lyn Cobley said the bank remained one of very few banks globally in the AA category.

"Since the onset of the financial crisis in 2008, the group has increased its capital base and improved its funding and liquidity position by increasing customer deposits and long term wholesale debt and reducing our use of short term wholesale funding," she said in a statement.

"At this point we do not expect this to have any material impact on our funding plans or expected pricing of our new issuance."

NAB chief executive Cameron Clyne said the bank was highly rated by global standards, well capitalised with strong funding and liquidity positions, and remains well-placed to continue to support customers.