The number of patients registered at health-board run practices in Wales has increased by 885% over the past five years, figures collected by the RCGP show.
Last year 151,431 patients were registered with a managed practice compared with 17,104 in 2012/13.
It means that now almost 5% of patients are covered by managed practices in Wales compared with 0.6% five years ago.
The news comes as the BMA has warned that health boards are running up large overspends as a result of running managed practices.
RCGP Wales said the figures highlight the pressure facing practices with many having been forced to hand their GMS contract back because they can no longer keep going.
A shortage of GPs has left other practices at risk of closure when partners retire or quit the profession.
The college said the figures were ‘further evidence of the need for the Welsh Government to dramatically increase the support available for general practice’.
Figures suggest the problem is most acute in North Wales, where data from 2017/18 show 12 managed practices serving almost 84,000 patients or 12% of the population.
Five years ago the region only had one practice run by the Betsi Cadwaladr University Health Board with 1,937 patients registered.
A small number of managed practices are in the process of returning to GMS status, including three in North Wales but the RCGP said the figures show the scale of the challenge.
Dr Peter Saul, RCGP Wales joint chair, said: ‘When workload pressures force practices into handing control to local health boards, the availability of appointments and continuity of care can suffer.
‘In those circumstances of forced transition there is a risk of increasing stress on other parts of the NHS, notably out of hours services.
‘There are also financial costs associated with practices being run by health boards.
‘Boosting the financial support for general practice would likely prove cost-effective in the long-term as it would keep more practices in the independent contractor model.’
He added that many practices are forced into handing back contracts because they have not been given enough support to manage rising demand and called for more investment in general practice.
‘Ultimately, these figures present further evidence of the need for the Welsh Government to dramatically increase the support available for general practice, in turn improving the care available for patients.’
Earlier this month, BMA Wales showed health board were overspending their budgets by millions to keep managed GP practices running, with some considering capping fees paid to GPs working for the practices.