Almost a quarter of trainee doctors say they are regularly forced to cope with situations beyond their clinical competence or experience, according to a new survey.
The General Medical Council (GMC) said 79% of junior doctors feel their training is excellent or good but warned there are "serious concerns that need to be tackled urgently".
The GMC's annual poll - The National Training Survey 2011 - found 22.9% feel "forced to cope with problems beyond their clinical competence or experience".
Of this figure, 1.9% said this happened on a daily basis, 9.8% on a weekly basis, and 11.1% on a monthly basis.
The GMC pointed out these figures have improved since last year's survey. The survey also found 25% of newly-qualified doctors say they do not feel ready to take the step to being a working junior doctor.
The questionnaire was completed by 46,668 doctors in training out of 53,674 who were eligible - a response rate of 87%.
The GMC said its research continued to show problems with the working time regulations which limited junior doctors to a 48-hour week in 2009.
It said almost two-thirds of trainees said they regularly worked more than this limit and 31% said it was taking them longer to meet the required competencies within the 48-hour working week.
GMC chief executive Niall Dickson said: "Trainee doctors are the future of healthcare in this country - the training they receive now will affect the care delivered in every hospital ward and GP surgery for years to come. The stakes are high. We simply must get it right."
Mr Dickson said: "In these difficult financial times for health service throughout the UK, it is vital the education and training are protected and that these young doctors are given the support they need not only to provide good care now but to develop into great leaders for the future."