"He attended this lab but asked his lab partner not to write his name on the assignment sheet. The lab partner did end up writing his name, as she assumed that he was a legitimate medical student."
It is understood he had been permitted to "interview" patients - but he did not treat them or have access to private records.
The source said the man's classmates had seen him wearing a student doctor identification badge. They were told yesterday that badge had been forged.
"He also had access to the medical school's cadaver dissection labs, including dissection of bodies donated to the medical school for medical student education.
"It is uncertain how he was able to obtain access to parts of the medical school buildings which are swipe card controlled," the source said.
Professor John Fraser, dean of the faculty of medical and health sciences, said: "Because of the size of the medical class, and by not submitting assessments or sitting tests, the individual was able to deceive classmates and teachers.
"This individual is not a student and is not on any class list. This person has not been given any confidential or restricted training material, and has not, to our knowledge, ever been able to examine any patients or received confidential patient information.
"We are investigating how this has happened and reviewing all procedures. The university is taking this very seriously."
Professor Fraser said the man's behaviour was "extremely unusual".
"This is the first such instance in the 43-year history of the medical school ... In view of this individual's actions and the likelihood of a police investigation, it is inappropriate for us to comment any further at this time."
Students on the same course have been offered counselling.
The matter has not yet been reported to police.
Medical misadventure
The Faculty of Medical and Health Sciences:
* Established in 1968.
* Has more than 4000 students studying across five schools.
* The schools are the School of Medical Sciences, the School of Medicine, the School of Nursing, the School of Pharmacy and the School of Population Health.
* The faculty is spread across two of the university's satellite campuses, Grafton and Tamaki.