The GP system in England is facing a "catastrophe" because of cuts in funding, doctors' leaders are warning.
Analysis by the Royal College of GPs suggests that over the past three years, investment in general practice has fallen by £400m in real terms.
That is equivalent to a 7% cut in spending per patient, it says.
Health Secretary Jeremy Hunt told the RCGP, which is meeting in Harrogate, he government wanted to increase access to GPs by extending opening hours.
On Tuesday, the prime minister said he wanted more patients to be able to get help in the evenings and at weekends, as he set out details of a £50m pilot programme in nine areas of England to widen access.
But the college said its analysis - based on official data from the Health and Social Care Information Centre - showed the government was taking money away from GPs despite claiming it wanted to move care away from hospitals.
The RCGP's chairwoman Dr Clare Gerada said the cuts meant doctors were being required to do more work with fewer resources, damaging services for patients.
In 2012-13, £8.5bn was invested in general practice, when everything from spending on pay, IT, tests and drugs was taken into account, it said.
That compared with £8.3bn in 2009-10, which is the equivalent of £8.9bn in 2012-13 prices.
In terms of spending per patient, that represents a fall from £168.40 a year to £156.45 - a drop of 7%.
Dr Gerada also pointed out that the investment represented 9% of the entire NHS budget, even though GPs had 90% of the contacts with patients.
She said: "Our figures should send out a warning to government and the rest of the NHS that we will soon have a catastrophe on our hands if urgent action is not taken to reverse the decline in funding.
"GPs are keen to do more for their patients, but we are heaving under the pressure of ever-increasing workloads and diminishing resources.
"Some of us are routinely working 11-hour days with up to 60 patient contacts in a single day and this is not safe or sustainable.
"You do not want a tired GP seeing you. You do not want a tired GP any more than you want a tired pilot or a tired surgeon."
Dr Gerada also expressed concern about the season ahead and said general practice was close to reaching a "tipping point" which would see the profession "fall over".
"We're trying to squeeze more and more activity out of a smaller and smaller pot of money," she added.
"If we have a cold winter, I'm really afraid that patients will suffer considerably.
"The front door of the NHS is the GP's surgery. If that gives, the rest of the NHS will give and very rapidly."
Health Secretary Jeremy Hunt, who addressed the conference on Thursday afternoon, did not object to the figures.
But he said the problems with investment in GPs "goes back further than three years".
"In the NHS we have invested in hospitals, in A&Es and we have not had a parallel investment in primary care."
He added the government was now looking to invest in programmes that increased access to GPs - hence the announcement this week to extend opening hours and increase the use of technologies such as email and Skype.
Patients Association chief executive Katherine Murphy said: "This chimes with what patients are saying to us. They are finding it harder to access GPs both in and out of hours.
"The mantra is about moving care out of hospitals and into the community, but if we are going to achieve that we have to stop throwing money at hospitals and invest in GPs so they can provide quality care."
Shadow health secretary Andy Burnham said: "These figures are embarrassing for a prime minister who got elected on a promise not to cut the NHS.
"They make a mockery of yet more promises he has made on GP access this week and show he simply can't be trusted on the NHS."