Washington DC - The US Federal Reserve's board named outgoing head Jerome Powell as temporary chair on Friday pending the swearing in of his successor, Kevin Warsh, who was confirmed by the Senate earlier this week.

"This temporary action to name the incumbent as chair pro tempore is consistent with past practice during similar transitions between chairs," the central bank said in a statement. Powell's second four-year term as chair ended on Friday.

He will now serve as temporary chair until Warsh, who was nominated by President Donald Trump and faced an arduous confirmation process, is sworn in.

The Federal Reserve has so far offered no date for when the incoming chair is to take his oath of office.

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On Wednesday, the US Senate voted 54 to 45 in favor of Warsh, with Republicans holding a slim majority and ensuring Trump's nominee was confirmed.

The process had earlier been held up by lawmakers over objections to a US Justice Department criminal investigation into Powell, which the outgoing chair had described as being designed to exert pressure on the Fed over monetary policy making.

In a statement, Fed Governors Stephen Miran and Michelle Bowman – both Trump nominees – said they approved Powell's appointment to a temporary term pending Warsh's induction, but did not support the term being indefinite.

"Given that we do not support an unlimited timeframe for temporary chair designation, we cannot support this action," they said.

"Given that we have a confirmed nominee who will soon be sworn in, in our view, the election of a chair pro tempore should be limited to a finite time period of at least a week (but we would support a period up to a month to allow for possible delay)."

Once known as a monetary "hawk" against inflation, Warsh has shifted in line with Trump's push for lower interest rates, which has posed an unprecedented challenge to the Fed's independence.

The incoming Fed chair, confirmed for a four-year term, has promised to bring "regime change" to the bank, which he has criticized as too political and too open in communicating its decision-making.

But with inflation still above the Fed's long-term two-percent target – and rising over Trump's Iran war – Warsh is unlikely to convince fellow members of the bank's rate-setting committee to cut immediately.