US agency Fitch has reaffirmed Australia's coveted AAA credit rating, but warned about the impact of a slowdown in the mining sector.

The credit rating reflects Australia's ability to repay foreign debt and is used to compare different countries.

Fitch says Australia has remained one of the strongest performing economies in the AAA universe since the global financial crisis.

It says a robust mining sector and demand for natural resources would continue to support Australia's economy.

Treasurer Wayne Swan says the AAA rating puts Australia in a select group of countries.

"Australia is one of eight countries to have a AAA rating from the three major global ratings agencies," he said.

"Why is all that important? Because the way some people are carrying on at the moment you'd swear that we were at the other end of the spectrum.

"It's important because what they are judging here is the underlying strength of the Australian economy.

"Low public debt, strong public finances, low unemployment, lower interest rates strong investment pipeline."

Fitch upgraded Australia to AAA for the first time in 2011.

However, the ratings agency warned about the mining slowdown and possible bank exposures in Australia.

"Ultimately, the key longer-term challenge facing Australia is how the economy will respond when mining sector investment peaks and begins to turn down," Fitch said in a statement.

"It is still too early to judge how the economy will perform once this stage is reached."

It also highlighted the potential for a downturn in asset prices or housing values.

"Large-scale problems in the banking sector, whether driven by a significant deterioration in asset quality (eg a sharp downturn in the housing market) or by a loss of access to international wholesale funding."

Fitch also noted the Government's plan to bring the budget back to surplus had been abandoned due to the strong Australian dollar and volatile commodity prices.

But the agency took the view that the process of fiscal consolidation has slowed rather than reversed.

Opposition Leader Tony Abbott has declined to comment.