Nearly every GP surgery in England is short of a family doctor, a leading medic has warned.
Professor Helen Stokes-Lampard said there is a "crisis" in the GP workforce.
Many doctors are so overwhelmed with workload pressures that they feel they are "not providing a safe enough service", the chairwoman of the Royal College of GPs said.
In an interview with the Press Association to mark the 70th anniversary of the creation of the health service, Prof Stokes-Lampard said there are promises of good things to come - including more GPs and extra funding for general practice - but it is still "very hard on the frontline".
She said work stress is leading some GPs to leave in the middle of their careers because "the system that has trained them has then broken them".
The GP Forward View published in 2016 said that by 2021, an extra £2.4 billion will go into general practice each year and the service would have 5,000 more doctors.
"We have got promises of good things coming but actually it is very hard on the frontline," Prof Stokes-Lampard told the Press Association.
"We have got fewer GPs now than we had when the GP Forward View was launched two years ago.
"Instead of needing the 5,000 we were promised then, we now need over 6,000 across England - that's basically a whole time equivalent GP for nearly every practice.
"There is intense frustration among professionals and that leads to stress and burnout.
"People know what they want to do for their patients, they know what they could do for their patients, but they are so overwhelmed by just the volume of work that needs to be done that they feel they are not providing a safe enough service. That's the workload pressure.
"It is shocking in many areas. This has led to a lot of burn-out and stress and people leaving the profession prematurely - which is part of the reason why we have got this workforce crisis and we have fewer GPs now.
"A lot of people have left and they have left at the middle stage of their career. As well as people retiring early we have got people giving up in the middle of their careers, which is a horrendous waste.
"There is not only the personal costs to those individuals, the system that has trained them has then broken them."
Prof Stokes-Lampard added: "Fundamentally we need to make the day-to-day job less stressful so that GPs can deliver the great care that they want to give in a service where they feel valued."
There are 7,271 GP practices in England and the latest workforce figures from NHS Digital in March show that in December 2017, there were 28,500 full-time equivalent GPs working in England.
On the anniversary of the creation of the NHS, Prof Stokes-Lampard said: "It is the nation's proudest achievement and so it should be for the future.
"There is no reason why we shouldn't be saying in another 70 years how proud we are of the NHS.
"Yes it is phenomenal and the reality is that if you do want a service like this then we have to pay for it, and a decision has now been made by the Prime Minister on our behalf that we do want to invest in it and we applaud her for that.
"I do think the proportion of money - while we welcome it very much as a step in the right direction - it is not enough for transformation and innovation that we need, it is enough to stabilise the service.
"That is going to be hard for people because announcements of big sums of money inevitably come with high expectations about what is going to change, it is going to take time."
NHS England chief executive Simon Stevens said pressures in general practice meant a lot of GPs were retiring early.
"Well we've actually now got record numbers of young doctors choosing General Practice for their speciality, which is fantastic," he told BBC One's The Andrew Marr Show.
"But the pressures in general practice mean that a lot of GPs are choosing to retire early.
"So part of what we've got to do is we've got to not just expand but we've got to redesign the way GP services work, relieving some of that load from them, including by more practice nurses and pharmacists and new technology."