Jerome Powell, chairman of the Federal Reserve, described this year's surge in US inflation as "temporary" and its ambiguous meaning has become a joke on Wall Street.

On Thursday, Powell broke away from the formulaic language and offered some insights into how long the factors driving up prices are likely to last.

At a hearing before the House Financial Services Committee on Thursday, Mr Powell said the economy was experiencing "very unusual events" in terms of supply constraints.

It is hard to see how long it will take to resolve the supply problem, he says. But "We expect these [restrictions] to weaken and inflation will fall over time."

"it is not clear when it will happen," Powell said. But I would like to say that we should see some relief in the coming months and the first half of next year.

Powell also said that inflation expectations were still in line with the Fed's 2 per cent inflation target "in a broad sense".

At the same hearing, US Treasury Secretary Janet Yellen said interest rates were likely to remain low even in the face of higher inflation. "most economists believe that low interest rates may continue to have deep structural reasons," Yellen said.