Junior doctors have started a 24-hour strike over a new pay and working hours contract, forcing thousands of routine operations to be cancelled.
Around 4,000 non-emergency operations have been rescheduled and appointments and tests will be affected, but medics will be providing emergency care and all A&Es will be open and running in the UK.
In the first of three strikes planned in January and February, around 38,000 members of the British Medical Association will take part in the industrial action on Tuesday.
Junior doctors' dispute in numbers
Junior doctors in England.
Days a week are worked by junior doctors.
Patients are dealt with every 36 hours by the NHS.
Days are worked annually by junior doctors.
Basic starting salary for a junior doctor.
£30,000 to £47,000
Basic salary for a doctor in specialist training.
Average total salary for a doctor in training, according to figures from the NHS Employers Organisation.
Junior doctors balloted by the BMA voted in favour of strikes, out of the 76% who participated in the poll in November.