Thousands of GPs working in outer suburbs and regional towns will see rebates from bulk-billing incentives drop by a third under a looming Medicare shake-up.

There is growing disquiet about the financial hit on doctors whose practices will be reclassified as metropolitan from January after changes to the rural classification system.

Some 2000 GPs will benefit — the result of gaining access to the $9.65 rural bulk-billing incentive for the first time.

But around 7000 GPs in places like Newcastle, Townsville and the outskirts of every capital city will see their incentives reduced from $9.65 to $6.40.