Earthquake survivor Kento Okuda, whose right leg had to be amputated when he was rescued, has been reunited with his family in Japan.

The 19-year-old arrived at Narita Airport on Monday. He was met by his mother and taken by ambulance to a Tokyo hospital for medical observation.

Kenichi Shibusawa, a 47-year-old priest who has been providing emotional and psychological support to distraught Japanese families in Christchurch, told a Japanese newspaper that Mr Okuda had suffered bouts of despondency, reportedly saying: "I don't know why I'm the only one who was rescued out of all those people who were trapped."

The Japanese Embassy says at least 27 Japanese nationals, including 12 from Toyama College of Foreign Languages who came to Christchurch with Mr Okuda, remain missing, feared dead.

More than 50 relatives and families of the students are in Christchurch waiting in anguish to find out if the bodies that have been pulled out from the Canterbury TV building are those of their loved ones.

A friend who had spoken to Mr Okuda before he left Christchurch Hospital said the rescued student was reluctant to leave.

"Kento said he felt guilty about leaving Christchurch without his schoolmates because they had made a vow to go back to Japan together after the earthquake struck," he said.

"He still cannot accept that his friends are dead because Kento said they were talking to each other while trapped under the flattened building."

Mr Okuda left Christchurch in a wheelchair, accompanied by a doctor from Japan on his Air New Zealand flight back to Tokyo.

A Yomiuri Shimbun report quoted Mr Okuda as tearfully saying: "I hope I can walk again as soon as possible."

Japanese deputy consul-general Mitsuko Ito says the decision to send Mr Okuda back to Japan was "strictly a medical one".

"He has received excellent care at Christchurch, but the doctors believe it would hasten his physical, psychological and emotional recovery if he was around family back in Japan."

Meanwhile, the other Japanese families in Christchurch are becoming increasing anxious and frustrated, says consul-general Hachiro Ishida.

"They are feeling very angry because there is not much information about their missing loved ones," Mr Ishida said. "But they are still co-operating with New Zealand authorities in the hope that it would speed up the identification process. Many of them just want closure."

The CTV site continues to receive intense international attention because of a large number of missing international students, including those from China, Thailand, Philippines, Taiwan and Czechoslovakia - but Japan remains the country hardest hit, outside of New Zealand.

A further 40 Japanese high school students studying at the Southern Cross language school were not injured, but also plan to return to Japan as soon as they can.

Japan's Foreign Ministry says 2820 Japanese are registered as living in Christchurch, but Japanese news reports say many have left the city since the quake.