Donald Trump on Sunday repeated his suggestion he might seek a third term as president, which would defy the two-term limit stipulated in the US Constitution.

In a Sunday morning phone call with NBC News, Trump said "I'm not joking," when asked to clarify a remark on seeking another term, adding: "There are methods which you could do it."

The 78-year-old billionaire has a long history of suggesting he might serve more than two terms, but Sunday's remarks — followed by comments to reporters aboard Air Force On — were the most concrete in terms of referring to plans in place to achieve the goal.

Trump has launched his second presidency with an unprecedented demonstration of executive power, using the world's richest man Elon Musk to dismantle swaths of the government, and said his supporters want even more.

"We have almost four years to go and that's a long time but despite that so many people are saying you've got to run again. They love the job we're doing," Trump said Sunday aboard the presidential jet, apparently referring to his political allies and supporters.

Trump appeared to wave off a reporter's question about whether he is planning not to leave office on 20 January 2029, the next Inauguration Day, saying: "I'm not looking at that, but I'll tell you, I have had more people ask me to have a third term."

Earlier in the day Trump told NBC he had been presented with plans that would allow him to seek reelection.

When the network asked Trump of a possible scenario whereby Vice President JD Vance would run for president and then abdicate the role to Trump, the president said "that's one" method.

He added that "there are others," but refused to share further details.

Amending the US Constitution to allow a third presidential term would require a two-thirds majority in both the House of Representatives and Senate, which Trump's Republican Party does not have, or a constitutional convention called by two thirds of the states that would propose changes to the charter.

Both routes appear to be unlikely, given the current number of states and Congressional seats under Republican control.

Whether he goes through Congress or the states, he would then require ratification from three-quarters of all state legislatures.

A constitutional convention has never been successfully called in the United States, where all 27 constitutional amendments have been passed by the congressional method.

In January, days after Trump took office, Republican Andy Ogles of Tennessee introduced a House joint resolution to amend the constitution to allow presidents up to three terms.