A prominent economic adviser to the prime minister says Tokyo should prepare for a "leaderless era" as U.S. global leadership gradually withers, and expand other strategic ties while bolstering its security alliance with Washington.

The prime minister, Yoshihide Suga, wasted little time in congratulating U.S. President-elect Joe Biden on last week's election win over incumbent Donald Trump, despite the latter's refusal to concede, saying he wanted to strengthen the alliance and ensure peace and prosperity in the Indo-Pacific region.

But concerns about America's inward turn have simmered in Japan for years, intensifying in the face of China's growing military and economic assertiveness and persisting during the Trump presidency despite comparatively warm ties between the outgoing U.S. leader and Suga's predecessor, Shinzo Abe.