Doctors are warning they are reaching breaking point as patient numbers in one city show an increase of 22% in a year.
A report says some are working as many as 70 hours a week and while the number of patients is going up, the number of doctors available to treat them is falling.
A report into primary care services report in Peterborough shows each doctor in the area has an extra 426 patients on their books compared to last year.
Dr Fiona Head, chief medical officer at the Cambridgeshire and Peterborough Integrated Care Service, said: "We are aware that people are complaining that they have difficulties getting through to their GP to make appointments, but GPs in our region are stretched to their breaking point.
"It is not that they don't work enough hours - many GPs work 60, 70 or even more hours a week - but the sheer numbers of patients per GP is rising all the time, and the number of GPs is, at the same time, falling."
Peterborough has the highest proportion of GPs and nurses over the age of 55 across the entire region, at 29% and 42% respectively.
Ms Head added: "Most of the GPs in the Peterborough area are, like myself, in their mid-50s or even older.
"They simply cannot see any change in their workload in the near future so that some of them are taking early retirement, while others have chosen to move away to different regions where the pressure on them is not so high."
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