LONDON (AP) — Thousands of junior doctors throughout England have gone on strike after the failure of contract negotiations.

The junior doctors will only provide emergency medical care during the 24-hour strike that started Wednesday morning. It's their second strike of the year — the work stoppage in January was the first such strike in 40 years.

The strikes are the result of a bitter contract dispute over pay and working conditions between the government and the British Medical Association. One of the key sticking points is a disagreement over payment for weekend shifts and whether Saturday should be treated as a normal working day.

National Health Service officials say several thousand medical procedures have had to be cancelled with many more likely to be affected.

Dr. Anne Rainsberry, national incident director for NHS England, said the national health service is doing everything possible to minimize the impact of the strike. She said it would delay care for "thousands of patients at a time of year when service pressures" are already at their highest.

Junior doctors are physicians who are in training. They can have up to 10 years of experience.