A changing population and old ways of providing care are creating a £4 billion funding gap and a "breaking point" scenario in London, according to health leaders.
A growing and ageing population, higher-than-ever patient expectations and zero financial growth means the NHS needs radical reform if it is to avoid the £4bn funding gap by 2020, Dr Anne Rainsberry, regional director of NHS England has warned.
Launching an analysis of the state of the capital's health and health services, the London region said the NHS must change the way services work or risk harming patient care - including increasing waiting times for treatments and limited or unsafe services at weekends.
Around 80% of premature deaths in London are attributable to lifestyle factors, such as alcohol, smoking, poor diet and a lack of exercise.
Life expectancy in London has risen by 5.2 years since 1990 - a year longer than the national average.
But stark variations exist between boroughs, and every two stops of the Jubilee line represents a year of life lost between residents of the most and least deprived areas, the organisation said.
The number of Londoners aged 65 and over is set to increase by 19% by 2020, and one in five children in London are at risk of obesity - higher than the national average - and mostly prevalent in London's poorest communities.
Despite rates of public trust in the NHS remaining relatively high compared to other national institutions, London has trends of low satisfaction levels.
London has poor rates of early diagnosis for diseases like cancer, NHS England said.
Around one in three cancer diagnoses are made in A&E, and it is estimated that London could save 1,000 more lives per year if early diagnosis rates equalled the best in Europe.
Meanwhile, the rate of acute sexually transmitted diseases is higher in London than in any other region.
Patients also want to see their GP more quickly - before and after work and at the weekend.
And many patients with long term conditions want to see their GP more frequently.
The NHS has to change so that routine services are more available, the organisation said.
Dr Rainsberry said: "We need to look more at how we can help people to stay well, rather than focusing on treating them once they are ill.
"Particularly for the increasing number of people living with long term conditions we need a step change in the way care is planned with patients and the way we use technology to support people.
"We have to do more with our existing budgets to keep the NHS free at the point of care. Based on our expectations of patient demands and that we expect a period of flat financial growth we are likely to have an affordability gap of £4 billion in London by 2020."
Dr Andy Mitchell, Medical Director for NHS England in London, said: "London's hospitals are at breaking point and the demand for healthcare will outstrip the funding available in just seven years unless we fundamentally change the way services are delivered.
"It is time to start listening to leading doctors and nurses about how we can adapt and change if the NHS is to survive.
"This will mean some difficult decisions need to be made."
The report will be published tomorrow.