AUCKLAND, June 19 - But the government says medical graduates have "exceptionally good" job prospects after uni.

A study in the New Zealand Medical Journal has found about 28 per cent of Kiwi medical graduates finish up with more than $90,000 of debt - a massive increase from a decade ago.

New Zealand Medical Students' Association says the problem occurs because medical degrees are expensive, at just over $15,000 a year in course fees, plus estimated average living costs of another $10,000.

On top of this, postgraduate students are only able to apply for loans to cover fees for eight years of university studies.

This means those who complete a separate degree before starting their medical studies often face a year or two at the end of their medical degree where they cannot apply for a student loan.

Association president Kieran Bunn said it was an "abysmal state of affairs" with the lobby aware of 30 students presently unable to apply for student loans for their final year of medicine.

"We desperately need doctors with a wide set of skills and from a wide variety of backgrounds to tackle the challenges of our future health system," he said.

But Tertiary Education Minister Paul Goldsmith said doctors earned more than twice as much as graduates in humanities and repaid their loans faster than all other student borrowers.

"Medicine remains an attractive career option for those who want one, from all backgrounds," he said.

"Universities have a number of scholarship opportunities available for students from low-income backgrounds. The costs can seem daunting while studying, but the financial benefits after graduation are significant."

He said medical students already received an extra year on their student loans, reflecting the disproportionate effect the standard seven-year limit had on them.

"Students who enter having already completed a prior undergraduate qualification are likely to use around [eight years] to complete the long qualification."