US President Barack Obama says he will oppose any attempt to undermine Japan's administration of disputed islands in the East China Sea, as he arrived in Tokyo for the start of his Asian tour.

The President has met Japanese Prime Minister Shinzo Abe to give a proposed regional trade treaty a much needed boost.

The Trans Pacific Partnership trade treaty would connect a dozen Asia Pacific economies, including Australia, by eliminating trade barriers and harmonising laws and regulations.

If realised it would be the biggest trade treaty in the world, covering two-fifths of the global economy and a third of all trade.

But wide gaps remained between the US and Japan when they held trade talks in Tokyo earlier this month.

Sorry, this video has expired Trade talks on President Barack Obama's trip to Asia ( Whitney Fitzsimmons )

"He's [Obama] going to really emphasise the importance to the United States and to the region for increasing trade and investment," said Dr Bates Gill, CEO of the US Studies Centre at Sydney University.

"He'll try to lay the groundwork for those difficult negotiations he's going to have to have back home with Congress."

Negotiating China

From Japan, Mr Obama will move onto South Korea, Malaysia and the Philippines.

All four countries on the President's itinerary are locked in separate territorial disputes with China.

Ahead of his arrival in Tokyo he said he would defend Japanese sovereignty over the disputed Senkaku islands in the East China Sea, known in China as the Diaoyu islands.

"China is, if you will, the elephant in the room on this trip," said Dr Jonathan Pollack, policy analyst at the Brookings Institute.

"He's not going to China, but one way or another, concerns about the rise of Chinese power and how it's perceived by others around the region will be on everyone's mind, including President Obama's."

The four Asian nations will be looking to the US for support.

"It's going to be a bit of a thorny and tricky context for the President. Expect some announcements in Japan, in South Korea as well as in the Philippines about an uptick in American military presence, including new rotations of troops," Dr Gill said.

As well as boosting security, Mr Obama will also be keen to follow up his recent efforts to cool long-standing tensions between Japan and South Korea.