Around 100 GP practices could be forced to close due to cuts in national funding, leaving patients in rural areas without a GP, doctors' leaders have warned.
Changes to how practices are paid mean some could no longer be viable, despite the fact some "provide vital services to thousands of rural patients", the British Medical Association (BMA) said.
It warned that large areas of rural England could be left with no GP practice for local residents.
The Government has decided to phase out a funding arrangement called the Minimum Practice Income Guarantee (MPIG) over a seven-year period, beginning in April.
MPIG means many smaller GP practices are guaranteed a minimum level of funding that is not dependent on the number of patients on their practice list.
NHS England has published an anonymised list of 98 'outlier' practices that could lose more than £3 per patient per year. Some practices on the list will lose more than £100 per patient per year while others stand to lose around £20 or £30 per patient.
NHS England denies that phasing out MPIG has a disproportionate impact on practices in rural areas. It argues that r ural practices make up less than 15% of the 98, while accounting for 18% of all practices in England.
The BMA said that in addition to the 98, there are a "significant number" of other practices that will be severely affected.
Dr Chaand Nagpaul, chair of the BMA's GP committee, said: "The Government has seriously misjudged the potential impact of its funding changes, especially on rural GP services.
"It is likely that a few hundred practices will lose noticeable levels of funding, with 98 practices identified by NHS England as being at serious risk from severe cuts in their financial support that could threaten their ability to remain open.
"This comes at a time when GP practices are already under pressure from rising workload and declines in overall levels of funding.
"The Government has not confirmed where these practices are or the extent of their financial difficulty, however some will be smaller GP practices in rural communities with comparatively small numbers of patients registered with them.
"These GPs provide vital services to patients in areas where accessing healthcare is already not easy because of the large distances patients have to travel to get to their local NHS services. If these practices were to close it could leave large geographical areas without a nearby GP practice.
"The situation has not been helped by NHS England's decision to devolve responsibility for this issue to local NHS managers without a framework on how these GP practices should be supported. We are without a national plan of how to tackle this problem and safeguard GP services.
"Ministers have to get a grip on this problem urgently, given these funding reductions are just weeks away from being implemented. We need to ensure no practice closes and that there is a co-ordinated approach to deal with this issue."
Dr Katharina Frey, who runs a rural practice in Cumbria, said: " My practice is a very small one that cares for just under 1,000 patients in a rural south Cumbrian area.
"We have for many years provided a real family-orientated service for patients and I believe we are a really vital service for our local community.
"We are under real financial pressure already and can't, because of the current funding climate, afford to employ a practice nurse.
"We are also having to think very carefully about how we replace senior staff. This situation will become even more pressurised when we lose the MPIG support that currently accounts for around a third of our current core funding.
"We are already working at full capacity with declining resources - I just don't know how we will cope with this additional financial blow."
An NHS England spokesman said: "NHS England is committed to making sure patients have access to high-quality GP services wherever they live and the GPs are properly funded to deliver these services.
"MPIG is not an equitable way of funding practices, which is why we are supporting its phased withdrawal. We believe it is fairer to allocate funds based on the numbers of patients practices serve and the health needs of those patients.
"We have looked very carefully at how the changes to MPIG, together with other changes to the general medical services contract, will impact on practices and we estimate that the majority will gain extra funding as a result.
"We also know that some practices will lose funding and we have asked our area teams to work with them to see how they can be supported. It may be that an alternative arrangement may be appropriate.
"This decision will be made by area teams after a full assessment of all the local circumstances."