Dec. 26 (UPI) -- Colleagues of a Chinese professor teaching at Japan's Hokkaido University of Education have filed a petition following his disappearance in China.
Yuan Keqin, who went missing about six months ago, was in China to attend the funeral of a family member, Kyodo News reported Thursday.
Akihiro Iwashita, a colleague, said in statement friends and associates have been unable to make contact with Yuan since the visit to China.
"There has been word Professor Yuan was undergoing care for high blood pressure," Iwashita said. "But so far there has been no communication."
Following his disappearance, Yuan's spouse had said her husband was staying in the Chinese city of Changchun while recuperating, according to South Korean newspaper Segye Ilbo on Thursday.
According to the university, Yuan's spouse has also become unreachable; it is unclear whether she is in Japan or China.
Yuan's hometown is Changchun, a city in Jilin Province not far from China's border with North Korea.
Yuan was born in 1955 and received his doctorate at Japan's Hitotsubashi University in Tokyo. He specializes in East Asian political history, the history of World War II and international relations of East Asia, according to reports.
In September, China detained Japanese professor Nobu Iwatani. Iwatani also teaches history and specializes in the second Sino-Japanese War and is a researcher of the Nationalist or Kuomintang Party.
Iwatani was released from Chinese custody ahead of the China, Japan and South Korea trilateral summit that concluded earlier in the week.
Yuan, a permanent resident of Japan, is a Chinese citizen.
"Please let us know if you have any information that can be confirmed, regarding Professor Yuan's condition in China," Yuan's colleagues wrote. "We sincerely hope Professor Yuan will safely return to Japan as soon as possible."
On Tuesday, China's foreign ministry said the government had received no confirmations regarding Yuan.