Public hospitals are struggling to retain a high number of overseas-trained doctors.

New Zealand has one of the highest proportions of overseas-trained doctors in the OECD, but research by the Association of Salaried Medical Specialists shows a third of international medical graduates are lost within five years.

Ian Powell, executive director of the association, said doctors are leaving due to poor working conditions - mainly uncompetitive salaries and a lack of support.

"After a year or three, they find the conditions not quite what they'd anticipated in many cases, so they leave," he said.

He says there is a need for urgent action by DHBs to ensure we have enough doctors now, and in the future.

"If we trained more and we retained more, we would be in a much better place," he said.

"We can still recruit internationally but we would not have the same level of dependence."