SEOUL: Pyongyang's relationship with Beijing is "invincible" because the countries both endured Japanese rule, North Korea said Saturday, the day after the Chinese President's highly symbolic visit ended.

The commentary, in official North Korean newspaper Rodong Sinmun, comes shortly before the G20 summit in Japan where US President Donald Trump will meet with China's Xi Jinping.

With Beijing and Washington at loggerheads over trade, China is keen to remind Trump of its influence with nuclear-armed Pyongyang, while increasingly looking to Japan -- a key US ally in the region -- to serve as a hedge against growing American protectionism.

Relations between Tokyo, Beijing, and both Koreas are still heavily affected by Japan's expansionism in the first half of the 20th century, with Pyongyang's state media criticising Japan on a near-daily basis.

Saturday's Rodong Sinmun dedicated five pages to the second day of Xi's visit to Pyongyang, and carried a separate editorial stating how the "sacred period of the anti-Japanese struggle has become the foundation of the DPRK-China friendship".

"DPRK-China relationship is an invincible friendship that firmly combines military camaraderie and trust," it stated, using the abbreviation of North Korea's official name.

Xi, in a rare opinion piece penned for the newspaper earlier this week, also said citizens of the countries jointly opposed a "foreign invasion" and supported each other in the pursuit of socialism.

Like North Korea, Beijing's Communist authorities also regularly denounce Tokyo over historical issues.

Xi is the first Chinese president to visit North Korea in 14 years, after relations deteriorated over Pyongyang's nuclear programmes and Beijing's subsequent backing of UN sanctions.

But when Kim embarked on a flurry of diplomacy last year, Xi -- as the leader of North Korea's main trading partner and key aid provider -- was the first head of state he met.

As Kim expands his diplomatic circle, Japan finds itself battling to remain involved in North Korean discussions.

Tokyo, one of the most hawkish of the major powers on the isolated North, has received some of Pyongyang's harshest rhetoric -- as well as missiles launched over its territory.

The dovish South Korean President Moon Jae-in -- who brokered nuclear talks between Washington and Pyongyang -- has also stressed the independence struggle against Japan is at the heart of both Koreas' national identity.

Seoul and Pyongyang's whirlwind of diplomacy has died down since a second Trump-Kim summit in February ended without a deal, and analysts say North Korea now may seek a new mediator for its deadlocked negotiations with Washington.

North Korea's official news agency KCNA also wrote Kim and Xi had reached agreement on "important issues" in their five summits over the past year. —AFP