Polling by the college as part of a campaign to make NHS GP services sustainable for the future found that 42% of 1,262 GPs and trainees who took part said they were likely to quit the profession in the next five years.
A workforce exodus on this scale would strip the health service of nearly 19,000 of the roughly 45,000 headcount GPs and GP trainees currently working in general practice.
RCGP chair Professor Martin Marshall warned that general practice was a profession in crisis - with the intensity and complexity of GP workload rising as the workforce continued to shrink.
He warned that 'alarming' findings from the RCGP poll must serve as a stark warning to politicians and NHS leaders over the urgent need for solutions to begin to tackle the crisis facing general practice.
The college called for a £150m annual GP retention fund, 10% year-on-year growth in GP training places and changes to visa rules threatening to drive out some UK-trained GPs.
It called for a review of GP contract arrangements and better co-ordination with secondary care to cut bureaucracy, better IT and an 11% share of the overall NHS budget for general practice as part of a package the college believes would improve access and continuity of care.
Alongside findings about doctors' intention to leave the health service, the college survey found that two thirds of respondents felt they lacked the time to 'properly assess their patients' - and 65% said patient safety 'is being compromised due to appointments being too short'.
Four in five respondents told the RCGP they expect working in general practice to get worse over the next few years - while only 6% expected things to improve.
Nearly two in five respondents said GP practice premises are not fit for purpose, and one in three said IT for booking systems is not good enough.
The college warned that even current record levels of recruitment into GP training - with 4,000 doctors starting GP training in 2021 - would 'not be enough to counter the numbers planning to leave the profession' even if all of these trainees enter the general practice workforce.
And the likelihood of all current trainees joining the ranks of fully qualified NHS GPs is low - BMA figures suggest one in eight GP trainees do not plan to work in general practice, and GPonline has reported on warnings that a lack of support with visas may leave many of the large proportion of GP trainees who are international medical graduates unable to stay in the UK.
Professor Marshall said: 'What our members are telling us about working on the frontline of general practice is alarming. General practice is significantly understaffed, underfunded, and overworked and this is impacting on the care and services we’re able to deliver to patients.
'The intensity and complexity of our workload is escalating whilst numbers of fully qualified, full-time GPs are falling. The college has been sounding alarm bells about the intense pressures GPs and our teams are working under, and the urgent need for support, since well before the pandemic, but COVID-19 has only exacerbated the situation. This is taking its toll on the health and wellbeing of GPs and other members of their teams - pushing many to consider leaving the profession earlier than planned.
'General practice is the bedrock of the NHS, keeping the service sustainable by making the majority of patient contacts, and alleviating pressures across the health service. But it is a profession and a service in crisis and needs urgent support.'
Professor Marshall said that measures set out in the college's report 'Fit for the Future: a new plan for GPs and their patients' would 'alleviate the unsustainable and unsafe pressure that GPs and our teams are working under'.
He added: 'Being a GP is a fantastic, stimulating and professionally satisfying career, when it is adequately resourced and when we have the time to deliver the care our patients need, and the type of care that we want to deliver. We need to make being a GP sustainable again, for the sake of the NHS, and for the sake of patients.'
BMA England GP committee deput chair Dr Kieran Sharrock said: 'This stark warning from the college is one that the government can ill afford to ignore.
'The number of fully-qualified GPs is already plummeting, meaning each day more people are losing "their family doctor", and such projections lay bare the potentially devastating impact for both the NHS and patients if politicians and policymakers fail to act.
'While GPs and their teams are doing all they can to ensure patients are seen at their practice when they need to be, current levels of workload are unsustainable and unsafe for both patients and staff. This will only worsen if we continue to haemorrhage doctors.'