Events are unfolding quickly on the Korean peninsula with planned summits between North and South Korea and the United States, a presidential official in Seoul said today, amid reports that North Korean leader Kim Jong Un is in China.

Bloomberg, citing three unidentified sources, reported yesterday that Kim was in Beijing in what would be his first known trip outside North Korea since taking power in 2011. The unconfirmed visit also comes ahead of a potential summit with US President Donald Trump.

"The presidential Blue House is watching things in Beijing very closely, while keeping all possibilities open," said the senior official in Seoul, who spoke on condition of anonymity.

Improving bilateral ties between North Korea and China would be a positive sign before the planned summits, he said.

A Reuters reporter saw a convoy leave Beijing's Diaoyutai State Guest House, where senior foreign leaders often stay on visits to the Chinese capital, and drive north on today morning. It was unclear where the convoy was headed.

Diplomatic sources in Beijing said it was likely Kim was in China, but they could not confirm it definitively.

One source with ties to China's leadership said it was possible Kim's sister, Kim Yo Jong (photo), was in the city. She visited South Korea for the Winter Olympics last month, paving the way for a summit between the two Koreas.

South Korean news agency Newsis reported that Kim Yo Jong and the North's ceremonial leader, Kim Yong Nam, were visiting Beijing, citing an unidentified North Korea-related source in Beijing.

The pair visited South Korean President Moon Jae-in at his office in Seoul during the Winter Olympics in February.

Purpose of visit unknown

The details of Kim Jong Un's visit, including its purpose and itinerary, were not yet known, Bloomberg reported. Japanese media reported earlier yesterday that a high-ranking Pyongyang official appeared to have arrived by train in Beijing.

The Blue House official said the South Korean government had been aware of "related movements" in North Korea, such as the train, for a few days but he could not confirm whether Kim or another high-ranking North Korean official was visiting China.

Beijing is secretive and isolated North Korea's main ally, as well as its biggest trading partner.

China has not confirmed any visit by a North Korean but has not totally censored speculation Kim himself might be in town.

Searches on Baidu News, China's equivalent of Google News, brought up a story in the simplified Chinese edition of Taiwanese newspaper The China Times that reported, without citing sources, that Kim was on a secret visit to Beijing.

There were also posts on Chinese social media talking about the possibility Kim was in China, some citing family members in the Chinese border city of Dandong where the main train link between the two countries is located.

Kim is due to hold separate summits with South Korea in late April and the United States in May, including a potential meeting with Trump.

"The fact that the summits are being held has been beyond our expectations. Right now, the situation surrounding the Korean peninsula is moving very quickly and it would be inadvisable to think with prejudice," the Blue House official said.

Kim Jong Un's father, Kim Jong Il, met then-president Jiang Zemin in China in 2000 before a summit between the two Koreas in June that year.

Kim Jong Il was considered at the time to have made the visit to reaffirm close ties with the North's biggest ally.

"North Korea likely wants to confirm its relationship with China and believes it has some leverage with which it can ask for things from China," said Yoo Ho-yeol, Professor of North Korean Studies at Seoul's Korea University.

"If North Korea speaks with the United States on its own it might feel it is at a disadvantage but, if it has China as an ally, Pyongyang may think it will be able to protect its interests and profits during the summits," Yoo said.

- Reuters