US President Donald Trump has raved about the warm hug he gave to Japanese Prime Minister Shinzo Abe and talked up the US-Japanese alliance, but the former reality TV star also warned their bond could falter.

Mr Trump and Mr Abe, who has enthusiastically pursued a relationship with the president, put on a united front at the White House on Friday.

They spoke out against North Korea’s missile and nuclear build-up and sent a message to China that the US and Japan would not allow freedom of navigation of ships in the South China Sea to be threatened.

Mr Trump also eased fears the US would militarily walk away from the Asia-Pacific region, instead, announcing the US would build up its military presence alongside Japan to make their defensive capabilities “impenetrable”.

“The US-Japan alliance is a cornerstone of peace and stability,” Mr Trump said.

“In the Pacific region it is important that both Japan and the US continue to invest very heavily in the alliance to build up our defence and defensive capabilities, which under our mutual leadership, will become stronger and stronger, and as time goes by ultimately they will be impenetrable.”

The Trans-Pacific Partnership free trade agreement between the US, Australia, Japan and nine other Pacific nations would not likely be a major talking point between Mr Trump and Mr Abe at the White House or when they fly to Florida and stay at the president’s Mar-a-Lago estate this weekend.

Mr Trump axed America’s involvement in the TPP in one of his first executive actions last month and said on Friday he was instead looking for a “free, fair and reciprocal” trade deal with Japan.

Mr Abe has perhaps been more aggressive than any other world leader in attempting to forge a relationship with Mr Trump.

The Japanese prime minister made a special visit to Trump Tower in New York just days after Mr Trump’s November election victory.

In the aftermath of recent fiery phone calls with Australian Prime Minister Malcolm Turnbull and Mexican President Enrique Pena Nieto, Mr Trump was on his best behaviour at the White House press conference with Mr Abe.

US President Trump walks with PM Shinzo Abe on their way to White House press conference. Photo: AAP

The Japanese leader also stroked Mr Trump’s ego by calling him an “excellent businessman” and, ahead of their golf game at Mar-a-Lago, told reporters “my scores in golf are not up to the level of Donald at all”.

“I grabbed him and hugged him because that is the way we feel,” said Mr Trump, describing the White House greeting he gave Mr Abe.

“We have a very, very good bond.
”

“Very, very good chemistry.”

But, just as Mr Trump the dealmaker is known to do, he halted the lovefest for a second to acknowledge that their best buddy relationship could falter.

“I’ll let you know if it changes, but I don’t think it will,” Mr Trump said.

– AAP