Beijing was under tight security Tuesday with speculation rife that North Korean leader Kim Jong Un was making a surprise visit, after the reported arrival from Pyongyang of a special train met by an honour guard.
If confirmed, it would mark Kim's first trip abroad since coming to power in 2011 and signal an intriguing twist in a fast-developing diplomatic exercise that has opened the door to separate summits between Kim and the presidents of South Korea and the United States.
Some analysts had suggested China -- the North's only major ally -- had been sidelined by the overtures from Pyongyang to Seoul and Washington, but a visit by Kim would put Beijing firmly back at the centre of the diplomatic equation.
Bill Bishop, publisher of the Sinocism China Newsletter, said President Xi Jinping likely wanted to meet with Kim before a summit with US President Donald Trump, which could take place in May.
"They're concerned about being left out, with the North Koreans directly cutting a deal with the Americans that doesn't necessarily reflect Chinese interests," Bishop told AFP.
A possible visit was first reported by Japan's Kyodo news agency, citing unidentified sources as saying that a high-ranking North Korean official had arrived in the Chinese capital on Monday.
Japanese broadcaster Nippon TV showed footage of a train -- similar to that used for foreign visits by Kim's late father Kim Jong Il -- pulling in to Beijing Station and being met by a military honour guard and a convoy of black limousines.
At the Diaoyutai guest house, where Kim Jong Il stayed during his visits to Beijing, there was an unusually heavy police presence with officers stationed every 50-100 metres in front of the imposing compound.
An AFP photographer saw a motorcade of limousines leave the guest house under a police escort on Tuesday morning.
There was also heightened security at two possible venues for a high-level meeting -- the Great Hall of the People and Zhongnanhai, the central leadership compound next to Beijing's Forbidden City.
There was no mention of any visit by either the Chinese or North Korean state media, and a Chinese foreign ministry official told AFP on Tuesday that it was "not aware of the situation".
China's Weibo micro-blog was censoring searches for Kim Jong Un's name and variations on it Tuesday. Beijing often tightens news controls during sensitive political periods.
South Korean broadcaster SBS TV said that guests at a hotel in the border city of Dandong, overlooking the train link from China to North Korea, had been asked to leave and curtains were drawn across the hotel windows.