The trip could be Kim's bid to "formalise" ties with Pyongyang's two main allies -- and potentially play a more prominent role on the international stage, experts say.

AFP takes a look at what we know:

- What's going on? -

Beijing is hosting a massive military parade on Wednesday to mark the 80th anniversary of Japan's surrender in World War II.

Kim and Putin are among more than 25 world leaders slated to attend, marking the first time the two men have appeared alongside Xi at the same event.

Their presence "formalises the China-Russia-North Korea trilateral (relationship) to the public", Soo Kim, a geopolitical risk consultant and former CIA analyst, told AFP.

"What better way to send a visual message to the rest of the world, notably the US, Japan, and South Korea, that this is indeed the trilateral they are up against?" she said.

- What might it mean? -

Nuclear-armed North Korea and Russia are traditional allies that have grown closer since Putin launched the full-scale invasion of Ukraine in 2022, with Kim sending weapons and thousands of troops to help Moscow.

"This not only earned Kim a sweet spot with Putin -- effectively, it also helped him strengthen his global positioning," Soo Kim said.

By deepening military cooperation with Russia, the North Korean leader was able to "emerge" from global isolation following years of heavy UN-led sanctions over his banned weapons programmes, she said.

China is Pyongyang's other major backer, and has also never denounced the Ukraine war -- drawing criticism from Western nations that it is tacitly supporting Russia.

The parade is "political theatre of the highest order... the primary message is the political solidarity of this new axis", Seong-Hyon Lee, a visiting scholar and associate at the Harvard University Asia Center, told AFP.

For Xi, the grand spectacle "cements his role as the undisputed leader of the anti-Western coalition", Lee said, adding that it also "shatters the narrative of (Putin's) diplomatic isolation".

- What does it mean for Kim? -

Kim enjoyed a brief bout of high-profile international diplomacy from around 2018, meeting US President Donald Trump and then South Korean President Moon Jae-in multiple times.

But he withdrew from the global scene after the collapse of a summit with Trump in Hanoi, Vietnam, in 2019.

Kim stayed in North Korea throughout the Covid-19 pandemic, but met Putin in Russia's far east in 2023.

Although Kim's grandfather, North Korea's founding leader Kim Il Sung, actively pursued global diplomacy, his father and predecessor Kim Jong Il was significantly more reclusive, said Cheong Seong-chang at Seoul's Sejong Institute.

Kim Jong Un's trip to Beijing could signal that, "like his grandfather... he will now become more active in foreign diplomacy", Cheong said.

Xi is also set to visit South Korea later this year for a major summit, and Kim's trip could signal an effort to hedge against the Chinese leader improving ties with Seoul's new president, Lee Jae Myung.

His China trip shows that Kim "feels more comfortable and confident as Russia-North Korea ties grow", Andrew Yeo, professor of politics at the Catholic University of America in Washington, told AFP.

- What about Trump? -

The Chinese parade comes as Trump steps up efforts to broker peace between Russia and Ukraine.

Trump -- who met Kim three times and once even said they had fallen "in love" -- has voiced hope of meeting him again.

Since their failed 2019 summit, Pyongyang has declared itself an "irreversible" nuclear state and recently rejected any suggestion of improving ties with Seoul's Lee.

Putin may even "serve as a useful go-between (for) Kim and Trump", Vladimir Tikhonov, Korean Studies professor at the University of Oslo, told AFP.

"Putin has been indicted for war-related crimes, but he is also perhaps the only contemporary power holder whom both Trump and Kim trust," he said.

- What will come afterwards? -

If Kim's Beijing trip is a success, it could help him score future diplomatic wins, Lim Eul-chul, a professor at the Institute for Far Eastern Studies at South Korea's Kyungnam University, said.

It opens up the possibility of a "reciprocal visit" by Xi to Pyongyang for a key anniversary in October, Lim told AFP.

Now that Putin and Xi are backing Kim, Trump's "calculus changes completely", said Harvard's Lee.

"The security guarantees provided by this new trilateral relationship effectively make North Korea's nuclear arsenal non-negotiable," he said.

"Kim is no longer just a recipient of aid. He has successfully leveraged his nuisance value into strategic relevance."