US President Trump has pledged close security and economic cooperation with Japan and called the alliance between the two nations "a cornerstone of regional peace and stability", edging away from campaign pledges to force Tokyo to pay more for the US' security umbrella.

Trump welcomed Japanese Prime Minister Shinzo Abe with a hug to the White House on Friday and shook his hand for a full 19 seconds where at one point Trump awkwardly jerked Abe's hand forward. The US President lavished praise on Abe and offered strong reassurances about America's commitment to Japan's defence, the New York Times reported.

"The bond between our two nations and the friendship between our two peoples runs very, very deep," Trump said at a press conference with Abe. "This administration is committed to bringing those ties even closer." 

"It is important that both Japan and the US continue to invest very heavily in the alliance to build up our defence and our defensive capabilities. I also want to take this opportunity, Mr Prime Minister, to thank you and the people of Japan for hosting our armed forces," he said.

Echoing his words, Abe also stressed on the importance of strengthening economic and trade relations. Abe also said that he would welcome the US becoming "even greater." The Japanese Prime Minister also invited Trump to visit Japan this year, which was accepted by Trump, according to the joint statement.

Japan also got continued US backing for its long-standing dispute with Beijing over uninhabited islands in the East China Sea, which China also claims. Trump said the US is committed to the security of Japan and all areas under its administrative control. The statement also said the two leaders affirmed that Article 5 of the US-Japan security treaty covered the islands, known as the Senkaku in Japan and the Diaoyu in China.

The two leaders were expected to discuss over the weekend Trump's decision to withdraw the US from the controversial 12-nation Trans-Pacific Partnership (TPP) trade pact, which Tokyo had lobbied hard for, according to reports.

A White House official said Trump was paying for Abe and his wife to travel to Mar-a-Lago Club in Florida for the weekend, as a "gift" to the leader. The two leaders would be playing golf there on Saturday.

Their Oval Office meeting came hours after Trump reaffirmed Washington's long-standing "one China" policy in a call with Chinese President Xi Jinping. 

Although Japan is a historic rival of China, Trump said that his long and "warm" conversation with Xi was good for Tokyo, too.

"I believe that will all work out very well for everybody, China, Japan, the United States and everybody in the region," Trump said at a joint news conference with Abe.

Abe is the second foreign leader Trump has met since taking office, after Britain's PM Theresa May.