US President Donald Trump said Tuesday (Nov 3) he will accept the results of the midterm elections where incoming figures indicate a Democratic wipe-out of his Republican Party in Congress.

"I am absolutely willing to accept those results," he told The New York Times. "We'll work with the Democrats, and we'll, you know, look forward to working with them. We'll probably work something out."

The conciliatory remarks came after repeated attempts by Trump to cast doubt over the fairness of the elections, adding to fears that he would refuse to accept defeat.

Earlier, the White House has said it was in a defiant mood, warning Democrats to "buckle up" and blaming some Republican candidates.

Trump himself had appeared agitated before the first results even came in, posting a string of angry messages on social media lashing out at conservative broadcaster Fox News's coverage.

But after initially saying Trump was "cautiously optimistic", the mood music changed as Democrats looked increasingly likely to deal the president a bruising setback that could upend his last two years in power.

"The White House mood is defiant," a White House official told AFP.

The official however questioned the quality of Republican candidates for the House and Senate - many of whom Trump had endorsed and travelled across the country to rally support for.

"Candidate quality matters, and President Trump did a better job promoting many of the candidates on the ballot than the candidates did themselves," the White House official said.

Trump was hosting his Cabinet officials and political advisers in the White House East Room for a reception to watch the results come in, the White House said.

Some White House staffers dined on take-out from US chain restaurant The Cheesecake Factory, in a dig at Democratic former president Barack Obama, who had said Trump's White House renovations were "looking like Saddam Hussein opened a Cheesecake Factory".

But journalists were not allowed into the watch party, and a bunker mentality increasingly appeared to be taking hold.

Polls repeatedly showed American voters were angered by Trump's Iran war and the resulting spike in the cost of living, but the White House dismissed those concerns.