Federal Reserve chair Janet Yellen has boosted the US dollar with hints of multiple interest rate rises, just days after President-elect Donald Trump talked the greenback down.

The US dollar had lost considerable ground earlier in the week, after Mr Trump said it was too high and making US manufacturers uncompetitive with Chinese firms.

However, the greenback rebounded this morning after Fed boss Janet Yellen pointed out that rates were likely to rise "a few times a year" for the next couple of years.

"As of last month, I and most of my colleagues – the other members of the Fed board in Washington and the presidents of the 12 regional Federal Reserve banks – were expecting to increase our federal funds rate target a few times a year until, by the end of 2019, it is close to our estimate of its longer-run neutral rate of 3 per cent," she said in her speech.

Analysts said that these comments confirm the Fed chair is equally hawkish as many of her committee members.

"In the wake of the recent Fed dots which showed the Fed's base case is now three hikes in 2017 many wondered if Yellen was aligned with this view," observed RBC Capital Markets chief US economist Tom Porcelli.

"It was a reasonable question given her dovish leanings over recent years.

"In a speech today she confirmed that she agrees with the base case."

That saw the US dollar rise, pushing the Australian dollar down to 75.09 US cents by 9:27am (AEDT).

US shares had a modest reaction to Dr Yellen's comments, with the Dow Jones Industrial Average down 0.1 per cent and the S&P 500 index up 0.2 per cent.