Hospitals are facing problems as 30,000 junior doctors start jobs in England, the British Medical Association says.
According to the BMA, operations and clinics will have to be postponed as NHS trusts rush to fill vacant posts “up to the eleventh hour”.
There are twice the normal number of junior doctors beginning jobs on Wednesday because of a shake-up which has ended staggered start days.
The government says NHS trusts have plans to ensure services run properly.
The changes to start days, under the Modernising Medical Careers programme, is designed to speed up the time it takes to become a consultant.
It follows reforms in junior doctor training and the introduction of the controversial online Medical Training Application Service (MTAS), which has proved unpopular with junior doctors.
Nine out of 10 doctors fear current medical training reforms and cuts in hours will cause standards to fall, a survey has found.
The British Medical Association (BMA) questioned more than 2,200 doctors across the UK for their views on the Government’s overhaul of training.
Modernising Medical Careers (MMC) is designed to cut the length of time it takes to qualify as a consultant. But doctors have expressed fears that the reforms will result in important skills being missed out of training.