North Korea’s ruler, Kim Jong-un, has arrived in Beijing at the invitation of Xi Jinping, seemingly to coordinate their countries’ approach for a summit with Donald Trump that could happen early this year.

Mr Kim will be in China until 10 January with his wife Ri Sol-ju, according to state media reports.

The visit comes amid reports that negotiations are under way for a second summit between Mr Kim and US President Donald Trump.

The two met last June, the first such meeting for a sitting US president.

Speculation had grown on Monday that Mr Kim was possibly making his way to China after South Korea's Yonhap news reported that a North Korean train had been seen crossing the border.

Dozens of security vehicles and officials blocked roads around the train station in the border town of Dandong.

Hotel guests in Dandong had also not been allowed to enter rooms that faced the border, with news outlet Kyodo calling this an "apparent move to prevent the train from being seen".

Both countries' media confirmed the visit on Tuesday morning. Mr Kim's distinctive green and yellow train arrived at a station in Beijing later in the day.

The train, the same one used during Mr Kim's first visit to China, resembles the one used by his father Kim Jong-il during his visits to China and Russia in 2011.

A motorcade with heavy security was later seen driving through central Beijing.

Mr Kim's visit, during which he is being accompanied by several leading North Korean officials, is his fourth to China in less than a year.

Tuesday is also reportedly Mr Kim's 35th birthday, though his date of birth has never been confirmed by Pyongyang.

China is an important diplomatic ally for North Korea, and one of its main sources of trade and aid.

"[Mr] Kim is eager to remind the Trump administration that he does have diplomatic and economic options besides what Washington and Seoul can offer," Harry J Kazianis, Director of Defense Studies at the Centre for the National Interest told Reuters.