U.S. President Barack Obama, left, is escorted by Japanese PM Yukio Hatoyama upon his arrival at the prime minister's official residence in Tokyo on Friday. (Issei Kato/Associated Press)

U.S. President Barack Obama and Japanese Prime Minister Yukio Hatoyama say they will renew their countries' five-decade-old alliance to confront new challenges, such as China's growing influence and North Korea's nuclear ambitions.

Opening a weeklong trip to Asia with a visit to Tokyo, Obama said Friday at a news conference with Hatoyama that he was confident the two leaders would "continue to strengthen the U.S.-Japan alliance so that it serves future generations."

The two leaders vowed to co-operate on climate change and to push for six-country multilateral talks concerning North Korea's nuclear program.

North Korea is one security issue where the U.S. and Japan share common ground, but Obama's visit comes at a time when other military matters are a source of tension between the allies.

Hatoyama came to power in September calling for a more equal partnership with the United States, and he has struck out in his own direction, committing to end the Japanese navy's eight-year-old Indian Ocean refuelling mission that supports U.S.-led troops in Afghanistan. Instead, Japan has committed to a $5-billion US civilian aid package in Afghanistan.

Hatoyama's comments Friday reflected that shift in tone, as he suggested the U.S.-Japan alliance must adapt to changing times.

Japan is also pushing to revisit a 2006 agreement to relocate a U.S. Marine Corps airfield in Okinawa to a less populated part of the island. Hatoyama now wants to move the troops off the island entirely and instead relocate them to Guam.

Hatoyama on Friday called the relocation of the U.S. military base from Okinawa a "difficult issue."

Obama will make a major speech Saturday in Japan on U.S.-Asia relations, and then will travel to Singapore for meetings at the Asia-Pacific Economic Co-operation summit.

From Singapore, he will travel to Shanghai, Beijing and Seoul before returning to the U.S.

With files from The Associated Press