The demand for doctors now outstrips supply to such an extent that in some parts of the UK more than 40% of NHS doctors have trained overseas.
A new report by the General Medical Council (GMC) has revealed that since 2012, the number of doctors on the register has increased by just 2%, while the number of A&E attendances has shot up by 27%.
In its State of Medical Education and Practice report, the GMC found the number of doctors training in the UK were unable to keep pace with the demands of an ageing population.
It said the medical profession was at "crunch point", with the NHS growing increasingly dependent on doctors who have trained overseas.
In the south-west of England, 18% of doctors are educated overseas, but in the east of England the number jumps dramatically to 43%.
The GMC said that NHS could face crisis if the UK becomes a less attractive place for foreign doctors to work in.
It also said the demands of training put off some people considering a career in medicine, and many doctors now want greater flexibility in how they work and train.
The report follows the launch of consultation by Health Education England on the future of the NHS workforce as a whole, which revealed it would have to fill a further 190,000 jobs by 2027.
On Tuesday, Labour published figures estimating that the NHS already has 100,000 vacant posts, with an average of 9% of jobs vacant across England's acute, community and mental health trusts.
This is a rise from 8.4% last year, Jonathan Ashworth, MP for Leicester South, found.
Information obtained by the party from 82 NHS trusts in England found that the average nurse vacancy rate was 12.2%.
After extrapolating the figures, it estimated that the health service across the country has more than 42,000 nursing vacancies.
The total of full-time equivalent vacancies for doctors was 9.3% - equating to more than 11,000 positions across the sector.
Charlie Massey, chief executive of the GMC, said in a statement: "We have reached a crucial moment - a crunch point - in the development of the UK's medical workforce. The decisions that we make over the next five years will determine whether it can meet these extra demands."
He added: "We are a professional regulator, not a workforce planning body, but we want to be an active partner in helping each country of the UK to address these priorities."
He said more needed to be done to "meet the challenges on the horizon".
The GMC's report emphasised that reducing the pressure on doctors and improving workplace culture and making employment and training more flexible would be vital steps to recruit and retain doctors in the future.
"The underlying challenge for all in healthcare is how we retain the good doctors we have right now," Mr Massey said.
"Everything we hear from the profession tells us that we need to value them more; nurture cultures that are safe and supportive, and do what we can to help staff achieve the right balance between their professional and personal lives through more flexible working arrangements."
Among the recommendations suggested by the GMC to reduce pressure and stress on doctors was a reform in the law to reduce the number of full fitness to practice hearings, particularly involving one-off clinical mistakes.