PRESIDENT Barack Obama said on Thursday that Donald Trump confirms his belief that the Republican is not qualified to be president "every time he speaks," adding that he was confident Americans would ultimately reject the brash billionaire on Election Day.

Ending his final presidential trip to Asia, Obama said his meetings with foreign leaders during stops in China and Laos had illustrated that governing is "serious business" requiring knowledge, preparation and thought-out policies that can actually be implemented. He urged Americans not to allow the "outrageous behavior" seen amid the campaign-season din to become the new normal.

"The most important thing for the public and the press is to just listen to what he says and follow up and ask questions to what appear to be either contradictory or uninformed or outright wacky ideas," Obama said.

Throughout the campaign, Obama has repeatedly denounced Trump and deemed him "unfit" to serve as commander in chief, while arguing that his controversial positions and comments are a step beyond what Republican nominees have embraced in the past. Obama has endorsed Hillary Clinton and has said he plans to campaign full-force for the Democrat before the Nov 8 election.

Obama's remarks came at the end of a grueling nine-day trip that took him to Laos and China following US stops in Nevada, Hawaii and Midway Atoll in the Pacific Ocean. Obama said the United States and Southeast Asian nations gathered in Laos have advanced a vision of an open, competitive economic system in which all nations play by the same rules.

"When I think back to the time I spent here as a boy, I can't help but be struck by the extraordinary progress that's been made by the region in the decades since, even if there's still a lot of work to be done," Obama said.

Topping that list is the Trans-Pacific Partnership, a 12-nation free-trade deal Obama helped broker. The deal awaits ratification in the US Congress, where there is opposition from both parties. Obama said he planned to do everything possible to persuade Congress to approve it before the end of the year.

Obama rejected the notion that he had been slighted while in Asia or that leaders in the region were rejecting his leadership - a criticism leveled by Trump.

The start of Obama's trip was overshadowed by tense moments on the tarmac in Hangzhou when Chinese officials clashed with White House aides and appeared to have failed to secure a staircase for Obama's plane. The awkwardness continued days later when Philippine President Rodrigo Duterte called Obama a "son of a bitch" and warned Obama not to challenge him in their planned meeting in Laos. Obama called off the meeting.

But Obama ended up exchanging pleasantries with Duterte on the summit's sidelines. Obama said they shook hands but that it was a brief interaction, adding that he had told Duterte their aides should confer on how the two treaty allies can move forward.

"I don't take these comments personally, because it seems as if this is a phrase he's used repeatedly directed at the pope and others," Obama said of the slur.

As an example of progress on the trip, Obama pointed to discussions with Southeast Asian leaders about maritime disputes in the South China Sea and suggested progress had been made in clarifying the path ahead to lower tensions between China and the Philippines. In a joint statement issued by leaders of the Association of Southeast Asian Nations, members were expected to issue a mild rebuke to China without referencing it by name.

"I realise this raises tensions," Obama said earlier as he met with ASEAN leaders, referring to a recent international arbitration ruling against China on the maritime dispute. "But I also look forward to discussing how we can constructively move forward together to lower tensions and promote diplomacy and regional stability."

On his final day in Asia, Obama met with Indian Prime Minister Narendra Modi, whose help Obama is seeking to galvanise further action on climate change, especially among developing countries. The two grinned and shook hands but made no substantive comments as reporters were allowed in briefly for the start of their meeting.