The visit comes three months after President Joe Biden and Prime Minister Fumio Kishida announced what they called a new era in Japanese-US relations at a summit at the White House.

Blinken and US Defense Secretary Lloyd Austin were due later Sunday to hold "2+2" talks with Japanese Foreign Minister Yoko Kamikawa and Defence Minister Minoru Kihara.

Then on Monday Blinken and Kamikawa will meet Indian Foreign Minister S. Jaishankar and Australia's Penny Wong, their counterparts in the Quad, an alliance seen as a bulwark against Beijing.

Prompted by unease about China and alarm about North Korea, Japan has in recent years been shedding its strict pacifist stance, ramping up defence spending and moving to obtain "counterstrike" capabilities.

This month Japan and the Philippines -- Blinken and Austin's next stop for a "2+2" -- signed a defence pact that will allow the deployment of troops on each other's territory.

This followed the first trilateral summit in April between the leaders of Japan, the Philippines and the United States in Washington.

Like with Manila, Japan and South Korea have also moved to bury the hatchet over World War II, with Biden hosting both countries' leaders at Camp David last August.

Due to join the talks in Tokyo this weekend was Shin Won-sik, the first South Korean defence minister to visit Japan in 15 years.

As part of the April announcement, Washington and Tokyo plan to upgrade their command structures -- at present the 54,000 US troops in Japan report back to Hawaii -- and improve the interoperability of their militaries to "deter and defend against threats".

On Sunday Austin will announce that the US will upgrade the current US Forces Japan headquarters, which is largely an administrative office, to an all-service or "Joint Force" headquarters led by a three-star commander, the Washington Post reported.

Sunday's talks were also set to cover enhancing Washington's "extended deterrence" commitment to use its military capabilities, including nuclear weapons, to protect Japan.

China's military modernisation, North Korea's nuclear and missile work and nuclear sabre-rattling in the Ukraine war have unsettled Japan, said Naoko Aoki, political scientist at the RAND think-tank.

"(It) is important for the United States to reassure Japan of its commitment and signal to potential adversaries that the alliance remains strong and that the United States is committed to using nuclear weapons if necessary to defend Japan," she told AFP.