Hundreds of thousands of Australians who currently pay nothing to see their doctor could face having to pay the full cost of their visit upfront as a result of the Abbott government's Medicare changes, a Senate committee has heard.

Health department officials told an estimates hearing late on Wednesday that it expects about 5 per cent of services to non-concessional patients which are currently bulk-billed would be privately billed following the changes, which are due to come into effect in July.

Greens senator Richard Di Natale believes hundreds of thousands of Australians will have to pay their full GP bill upfront. Credit:James Boddington

This would mean that these patients would have to pay the full cost of the visit upfront, and make their own claim for a rebate from Medicare.

From July, the government is proposing to cut the Medicare rebate for GP visits for non-concessional patients by $5, and allow doctors to recoup the loss by charging patients a fee of up to $5.