More than 2,000 doctors at 50 university hospitals in Japan have been working without pay, and many lack employment contracts or compensation insurance, the education ministry said Friday, based on a recent survey.

"The findings are very regrettable, and it is only natural to correct the practice of not rewarding doctors who should be paid," education minister Masahiko Shibayama said.

Japanese university hospitals have a practice of not paying wages to doctors who treat patients as part of research or training, as many of them are graduate students.