Donald Trump has touched down in Tokyo in the first leg of his five-nation tour of Asia, which comes as concerns grow about North Korea's nuclear and missile programs.

It's the US president's first swing through a continent gripped with tension over a nuclear standoff on its eastern edge.

He'll carry out high-stakes talks with the leaders of Japan, South Korea, and China and attend summits in Vietnam and the Philippines.

President Trump's begun by rallying American and Japanese forces at an air base near Tokyo, talking up the prowess of the US military and its allies in the region.

"We dominate the sky, we dominate the sea, we dominate the land and space."

He told the gathered troops he is honoured to be in a beautiful country.

"Japan is a treasured partner and crucial ally of the United States and today we thank them for welcoming us and for decades of wonderful friendship between our two nations."

During his three day stay in Japan, the US president will play golf with Prime Minister Shinzo Abe, hold talks with him and meet Emperor Akihito and Empress Michiko.

About 21,000 police officers have been mobilised to ensure security in and around Tokyo.