AUCKLAND, June 21 - The New Zealand Medical Students' Association has called for an eight-year cap on student loans to be lifted for its members, saying at least 30 students currently faced the prosect of not being able to get loans for their final year.

The limit means some students with previous degrees could be left to pay fees of $15,000 a year plus living costs without a loan, the association said.

Now the New Zealand Medical Association has backed that appeal.

"The cap on student loans limits the pool of people undertaking medical training to those with financial resources, and cuts out many with prior education or training in other fields, who may be ideal candidates," NZMA chair Kate Baddock said.

"With a cap on student loans at eight years of full-time study, we risk losing many of those whose experience and knowledge - beyond the confines of medicine - could significantly benefit our patients and the health of all New Zealanders."

But Tertiary Education Minister Paul Goldsmith this week said medical students already received an extra year on their student loans, reflecting the disproportionate effect the standard seven-year limit - applied to other students - 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," he said.

Doctors also earned more than twice as much as graduates in humanities and repaid their loans faster than all other student borrowers, Goldsmith said.

"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."