SEOUL, South Korea >> North Korean leader Kim Jong Un is making a four-day trip to China, the North’s state media reported Tuesday, in what’s likely an effort by Kim to coordinate with his only major ally ahead of a summit with U.S. President Donald Trump that could happen early this year.

Kim departed for China on Monday afternoon with his wife Ri Sol Ju and other top officials, the North’s Korean Central News Agency said. It said Kim is visiting China at the invitation of Chinese President Xi Jinping.

South Korean media reported that Kim’s distinctive armored train was expected to reach Beijing on Tuesday morning, which happens to be Kim’s birthday.

China’s official Xinhua News Agency issued a nearly identical report, while Beijing’s North Railway Station was cocooned in security, with dozens of police and paramilitary troops patrolling outside. What appeared to be official cars were seen driving past the security cordon into the station, although journalists on the scene were too far away to identify them clearly.

Kim is expected to stay at the highly secure Diaoyutai State Guest House in the capital’s west, with meetings held at the Great Hall of the People, the hulking seat of the legislature that sits next to Tiananmen Square.

The trip marked a further break with past practice in that it was announced in advance of Kim’s arrival, a possible sign of growing confidence on the part of North Korea and its most important ally, China.

After years of cool relations following Kim’s assumption of power 2011, ties have improved remarkably over the past year as Xi seeks to maintain his influence in the region.

Kim’s trip comes after U.S. and North Korean officials reportedly met in Vietnam to discuss the location of a second summit between Kim and Trump as the two nations look to settle the North’s decades-long pursuit of a nuclear arsenal.

Washington and Pyongyang seemed close to war at points during 2017 as the North staged a series of increasingly powerful weapons tests that got it tantalizingly close to its nuclear goal of one day targeting with pinpoint accuracy anywhere on the U.S. mainland

Possibly fearing the economic effect of crushing outside sanctions imposed because of his weapons’ tests, Kim abruptly turned to diplomacy with Seoul and Washington last year. Three times he visited China, which is North Korea’s most important trading partner and a key buffer against pressure from Washington.

But even after what was seen as a blockbuster summit between Kim and Trump in Singapore last June — the first-ever between the leaders of the war enemies — there’s been little real progress in nuclear disarmament.

Washington is pressing the North to offer up a detailed accounting of its nuclear arsenal, while Pyongyang says it has already done enough and it’s time for the U.S. to ease harsh international sanctions that hold back the North Korean economy.

Despite Trump’s repeated assurances that another summit will allow he and Kim to make a grand deal to settle the nuclear standoff and change a relationship marked by decades of animosity and mistrust, outside analysts are highly skeptical that the North will easily abandon a nuclear arsenal constructed in the face of deep poverty and likely seen by Kim as his only guarantee of regime survival.