The medical expert said during a visit to the countryside earlier this month, Kim clutched his chest and fell to the ground.
A doctor accompanying Kim immediately carried out CPR and took him to a nearby hospital for emergency care.
China has dispatched a team to North Korea including medical experts to advise on him, according to four people familiar with the situation.
Reuters was unable to immediately determine what the trip by the Chinese team signaled in terms of Kim's health.
However Shukan Gendai's report claims they were called to the leader's aid by his accompanying doctor after the incident.
When Kim Jong Un's father, Kim Jong Il, suffered a stroke in 2008, South Korean media reported at the time that Chinese doctors were involved in his treatment along with French physicians.
Kim is a third-generation hereditary leader who came to power after his father Kim Jong Il died in 2011 from a heart attack. »