The US ambassador to Japan says that under Japanese Prime Minister Kishida Fumio's "steadfast leadership," the two countries have ushered in a new era for the bilateral alliance.

Rahm Emanuel posted a message both in English and Japanese on social media on Wednesday following Kishida's announcement that he will not run in the ruling Liberal Democratic Party's leadership election next month.

Emanuel wrote, "Today, the Alliance is stronger and more secure than at any time in its 64-year history."

He also noted that, working side by side with US President Joe Biden, Kishida "helped build a latticework of security alliances and partnerships across the Indo-Pacific region that will stand the test of time."

Chinese media reported Kishida's announcement as breaking news, citing Japanese media.

A Tokyo-based reporter for state-run China Central Television said the approval ratings of Kishida's Cabinet declined as Japanese voters became increasingly dissatisfied with several issues. They were the political funding scandal involving LDP factions, recent inflation and the weakening of the yen.

The reporter said this may have been one of the reasons Kishida decided not to run in the leadership race.

Australian Prime Minister Anthony Albanese posted a photo on social media of himself shaking hands with Kishida.

He wrote that Kishida "has always valued the vital relationship between Japan and Australia, and his leadership has helped strengthen it."

Albanese concluded his message by wishing Kishida "all the very best for the future."