Satellite images appear to show a train likely belonging to North Korean leader Kim Jong-un has been parked at his compound on the country's east coast since last week.
The images come amid speculation about Kim's health, caused in part by a long period out of the public eye.
Kim Jong-un is in "a vegetative state" in a coma following a botched heart operation, according to disputed reports.
The unverified claims – which follow online rumours of his death – emerged as a team of Chinese medical experts reportedly flew in to treat the North Korean despot, who has not been seen in public for two weeks, reports the Sun.
Rumours intensified about Kim Jong-un's condition as the Chinese team including health care experts was dispatched into North Korea to treat him, Reuters reports.
The trip by Chinese doctors and officials to Pyongyang comes after reports the North Korean leader was in a critical condition after cardiovascular surgery.
A delegation including the medical staff and led by a senior member of the Chinese Communist Party's International Liaison Department left Beijing for North Korea on Thursday.
The New York Post is reporting a vice-director of HKSTV Hong Kong Satellite Television, a Beijing-backed broadcast network in Hong Kong, claimed that Kim was dead, citing a "very solid source".
Her post on the Chinese messaging app Weibo has been shared widely on social media, according to a report in the International Business Times.
The satellite photos released by 38 North, a website specialising in North Korea studies, don't say anything about Kim's potential health problems, and they echo South Korean government intelligence that Kim is staying outside of the capital, Pyongyang.
Kim Jong-un's train has been parked at the Leadership Railway Station servicing his Wonsan compound since at least April 21, website 38 North reports, citing an analysis of recent satellite photos of the area.
The website said that the approximately 250m-long train wasn't present on April 15 but was present on both April 21 and 23.
"The train's presence does not prove the whereabouts of the North Korean leader or indicate anything about his health, but it does lend weight to reports that Kim is staying at an elite area on the country's eastern coast," it said.
North Korea exerts extremely tight control on information about its leadership, making it virtually impossible for outsiders to find out what's going on at those senior levels.
Seoul has also repeatedly indicated that there have been no unusual signs that could indicate health problems for Kim.
That hasn't stopped growing unconfirmed rumours and media reports about Kim's health that have emerged since he missed an April 15 commemoration of the 108th birthday of his grandfather and North Korea founder, Kim Il-sung.
Earlier in the week, South Korean news site Daily NK reported Kim was recovering after undergoing a cardiovascular procedure on April 12.
US officials said they were told Kim's condition was critical after the surgery, although President Donald Trump has since cast doubt on the report.
On Saturday there were reports from Japan that the North Korean leader was in a "vegetative state".
Speculation about Kim's condition has escalated in the two weeks since he was last seen in public, at a politburo meeting on April 11.
Kim Jong-un is the third generation of his family to rule North Korea, and he hadn't missed the April 15 commemoration event, one of the year's most important for the North, since assuming power after his father Kim Jong-il's death in late 2011.
On Thursday, Trump told reporters he thought the report Kim was gravely ill "was incorrect" but declined to say if he had been in touch with North Korea.
US Secretary of State Mike Pompeo told Fox News when asked about Kim's health, "I don't have anything I can share with you tonight, but the American people should know we're watching the situation very keenly".
Kim, whose age is either 36 or 37, is said to be a heavy smoker, and has gained weight since he succeeded his father in 2011.
He also may have hereditary cardiovascular disease.
Kim's health is of crucial importance because of worries that the serious illness or death of a leader venerated with near godlike passion by millions of North Koreans could cause instability in the impoverished, nuclear-armed country.
A US official, speaking on condition of anonymity because he wasn't authorised to talk to the media, said the latest rumours about Kim's health had not changed the US assessment of the information as "speculation."
White House counsellor Kellyanne Conway wouldn't comment on Kim's status.
"The President will make any announcement about a head of state," she said on Saturday night on Fox News Channel's Justice with Judge Jeanine.
Danny Russel, a former National Security Council director and assistant secretary of state for Asia who has dealt with North Korea in the past, cautioned that rumours have abounded for years about Kim, his father and his grandfather and most turned out to have been false.
"While serving in government I was on the receiving end of multiple intelligence reports about alleged accidents, illnesses and assassination attempts against North Korean leaders — only to have them reappear in public," he said.
South Korea's presidential office said last week that Kim appeared to be handling state affairs normally and that there had been no suspicious activities, such as an emergency readiness order issued by the North's military or the ruling Workers' Party. The South Korean government has since maintained its assessment that Kim's health remains the same. Some South Korean media outlets, citing unidentified government officials, have reported that Kim was staying at Wonsan.
North Korea's state media have been silent about the speculation on Kim's health. On Saturday, the North's official Korean Central News Agency reported that Kim had received a message of greetings from the chairman of the Central Committee of the Communist Party of the Russian Federation on the occasion of the first anniversary of Kim's summit with Russian President Vladimir Putin. The message wished Kim "good health and happiness", KCNA said.
It's not the first time that Kim has vanished from the public eye, and past absences in state media dispatches have also triggered speculation about his health. In 2014, state media didn't report any public activities for Kim for about six weeks, before he reappeared with a cane. South Korea's spy agency said later that he had a cyst removed from his ankle.
Many experts in South Korea downplayed speculation that Kim was seriously ill. They also said North Korea won't likely face a serious immediate turmoil even if Kim was incapacitated or died because someone else like his influential sister Kim Yoo Jong would quickly step in, though the prospect for the North's long-term political future would be unclear.
In 2008, Kim Jong-il suffered a stroke and was reportedly treated by Chinese and French medical specialists.
He died in 2011 from a heart attack at the age of 70.
North Korea's founder Kim Il Sung, who the current Kim closely resembles, ruled the country until his death in 1994, aged 82.
Trump made history when he met Kim Jong-un, in Singapore in 2018, for the first-ever talks held between a North Korean leader and a sitting US president.
- with AP