Aust downgrade will hit AAA states:S

S&P says a downgrade of Australia's AAA rating would only impact on the ratings of similarly rated states of NSW, Victoria and the ACT.

A cut to Australia's triple-A rating would only flow-through to the ratings of the AAA states of NSW, Victoria and the ACT, a global ratings agency says.

So it wouldn't automatically affect Queensland, Western Australia and Tasmania - which are all rated AA-plus - or the AA rated South Australia, Standard & Poor's global ratings analyst Anthony Walker said.

"This is because their credit ratings are lower than the Australian sovereign and already incorporate our view that their credit quality is slightly lower than that of the sovereign," he said in a report released on Tuesday.