The arrival of a train in Beijing has fuelled speculation that North Korean leader Kim Jong Un is visiting China.
Reports from the Chinese capital said the train was met with heavy security when it arrived on Monday, and suggested a high-level official from the secretive state was on board.
A convoy was then seen travelling to the Diaoyutai State Guesthouse, where North Korean leaders have been known to stay in the past.
Photos of the train were shared by Japanese broadcaster Nippon TV.
Intriguing images from Beijing, captured by Japan's Nippon TV. A 21-car train, similar to one used by Kim Jong Il in 2011, pulled into Beijing Station around 3pm. Met by honor guard and line of VIP cars. Speculation is that Kim Jong Un could be in Beijing. https://t.co/OR40pYEcgG pic.twitter.com/1G5jndciIr
— Martyn Williams (@martyn_williams) March 26, 2018
Bloomberg cited unnamed sources as saying Mr Kim was indeed making a surprise visit to Beijing.
However, neither Chinese nor North Korean officials have confirmed a state visit is under way.
A South Korean official told Reuters the government there was "watching things in Beijing very closely".
The current North Korean leader's predecessor and father Kim Jong Il visited Beijing in 2011, shortly before his death - and during that trip he travelled on board a train similar to the one seen in Beijing this week.
China remains the most high-profile ally of the North Korean regime.
The reported diplomatic visit would mark Kim Jong Un's first known foreign trip since taking office more than six years ago.
It also comes ahead of the planned meeting between Mr Kim and US President Donald Trump in May.
A recent visit by high-level North Korean diplomats to Sweden sparked speculation that the country could be used as a venue for the extraordinary meeting.
Despite Mr Kim and Mr Trump trading insults and threats over the last year, the US leader has accepted an offer to meet his North Korean counterpart after the invite was made via South Korean diplomats.
Kim Jong Un talked about denuclearization with the South Korean Representatives, not just a freeze. Also, no missile testing by North Korea during this period of time. Great progress being made but sanctions will remain until an agreement is reached. Meeting being planned!
— Donald J. Trump (@realDonaldTrump) March 9, 2018