The GP system stands "on the brink of collapse" and would go the way of dentistry under another term of the Tories, Wes Streeting has said.
The shadow health secretary said a Labour government would divert billions of pounds from hospitals in an attempt to save "the front door" of the NHS and ensure patients could get help sooner.
In an interview with The Telegraph, Mr Streeting said an incoming government would be "far more assertive" in questioning how the £170 billion NHS budget is spent, and shifting far more resources into services in the community.
Mr Streeting said the GP system was now "on the brink of collapse" and would "go the same way as dentistry" within five years if the current Government remained in power.
New analysis of official data shows that one in six patients failed to secure an appointment with their GP last year. Around five million patients a month were left without a slot, up from 2.45 million in 2021, Labour said.
The forecasts also suggest that on current trends, the number forced to wait at least a month would triple in the next five years, leaving another five million facing such waits.
Mr Streeting said: "If the Conservatives get in, general practice will become a poor service for poor people, while those who can afford it pay to go private and others just get priced out altogether".
The shadow health secretary said improving access to family doctors and community services was key to easing the wider crisis across the health service and lifting pressures on hospitals.
He said: "It's at the crux of the crisis in the NHS because, unless we fix the front door to the NHS in general practice, we're not going to get the rest of the system working."
He added: "I genuinely think general practice is on the brink of collapse," and pledged to "bring back the family doctor" and to "rebuild the relationship between GP and patient".
Under Labour's plans, GP practices that provide better continuity of care and allow patients to see the doctor of their choice will receive higher funding than other surgeries. The party also pledged to train thousands more family doctors, update the NHS app and cut red tape as part of efforts to end the "8am scramble" for an appointment.
Separate research published on Tuesday shows a sharp fall in the number of patients able to see the GP of their choice.
The study by the University of Leicester, which analysed data from more than 6,000 practices in England, found that in 2022, just 19 per cent of patients were able to see their preferred doctor - down from 29 per cent in 2018.
Mr Streeting said it was not just billions of pounds which would be diverted from hospitals to GP services, but also many of their functions.
"It's not just money, but services, too," he said. "A lot of secondary care leaders responsible for our big hospitals recognise that the solution to the A&E delays, the ambulance handover delays, the discharge delays when hospitals are clogged up lie outside of the hospital in primary care and community services. We've listened to those calls and that is where our focus is going to be."
Pilot schemes of Neighbourhood Health Centres - one-stop shops bringing together GP practices with physiotherapists, nurses, care workers and health visitors - would be trialled across the country, under the plans.
Mr Streeting accused critics of "breathtaking complacency" in assuming that Labour could not turn around the performance of the NHS without a major cash injection.
A recent analysis by the Nuffield Trust forecast that Labour and the Conservatives would both leave the NHS with lower spending increases than during the years of Tory austerity.
"During this election campaign, we've taken some flack, particularly from the think tanks, because Labour doesn't have a big spending manifesto when it comes to health. But I think - and I say this with respect, that think tank analysis speaks to the breathtaking complacency and groupthink, amongst the health establishment who think that the first answer is always more money, without first questioning how almost £170 billion of taxpayers' money has already been spent," he said.
"You talk to the patients who are using the system, the staff working in the system - they can see examples every day of waste, inefficiency and bureaucracy."
A Conservative Party spokesman said: "If Labour really had a plan to improve GP services, they would be delivering it in Labour-run Wales. Instead, one in five GP surgeries have closed in the past decade and NHS waiting lists are at a record high.
"The Conservatives have already recruited 2,700 more full-time GPs and met our manifesto commitment to deliver 50 million extra GP appointments since 2019.
Earlier this month, Mr Streeting was accused of having "let the cat out of the bag" when he admitted that Labour's manifesto was not the "sum total" of its spending plans.
He now suggests that a pay rise for junior doctors is likely to be one of the first areas to stretch spending beyond existing commitments.
As junior doctors prepare to launch their eleventh round of strikes on Thursday, with five days of walkouts ahead of the general election, Mr Streeting said it was in the country's interest for the Government to "cut a deal".
Mr Streeting said: "This dispute has meant over a million operations appointments and procedures being delayed or cancelled and it has cost the taxpayer £3 billion - that is a hell of a lot of money to pay for failure.
"So it is in our interest to cut a deal and we're going to have to look at what we can do as far as the books allow."
The shadow health secretary said he had made clear to the British Medical Association that its demands for a 35 per cent pay rise were "not something that the country could afford".
But he said the union had shown "a willingness to negotiate down from 35 per cent to recognise that pay restoration is a journey, not an event."