The US economy is humming under President Donald Trump - but is it sustainable?

S&P Global US chief economist Beth Ann Bovino says the US economy was doing well before the Trump administration took over the helm.

In the last quarter the US economy experienced 4.1 per cent GDP growth.

"When we look at the US economy we have job gains holding at around 200,000 jobs per month ... you have people spending, you have businesses investing significant amounts and that's all a positive thing but the worry of course is that the tax package and also the bipartisan budget agreement that also came in to place, the question is; 'are we going to see the productivity boost or are we going to just see inflation down the road?'," Bovino said.

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Economists expect US growth to slow down by 2020.

At present, the trade war between had not affected US business, she said.

"In terms of the impact from the trade dispute that's in place, some call it trade war, some call it dispute, I would say that the impact on the US and probably China as well - they are the two biggest economies in the world, is going to be rather small.

"The worry we have in terms of the trade war is what happens if we start to see the secondary effects; if we start to see businesses get spooked."