NHS consultants and junior doctors will strike together for the first time this week.
Doctors from the British Medical Association will leave almost all hospital departments on Wednesday as most operations are canceled and the emergency department and wards are only covered on “Christmas Day”.
Health bosses say it will be the worst staff protest they have ever seen.
Consultants start tomorrow, Tuesday, with two days of strike action.
The junior doctors follow on Thursday and Friday and the “Double-Whammy” on Wednesday.
Saffron Cordery of NHS Providers, who represents hospital bosses, warned on BBC Breakfast: “We are now in uncharted territory.”
She said: “This will have a very worrying impact on services.”
“Patients are the ones who suffer when it comes to quality of life when their appointments, surgeries and procedures are postponed.”
“I think there is a real danger now that everything will become normal.”
“It has to end before we become fully entrenched in winter.”
Downing Street said on Monday: “These coordinated strikes will pose a major challenge to the NHS and patients, whose care will be significantly affected.”
The BMA is pushing for a bigger pay rise for doctors after members said the increase given by ministers over the summer was not enough.
The government refuses to give in, but its promise to reduce the waiting list is being destroyed by the strikes.
There are currently a record 7.7 million people waiting for treatment in England, with numbers rising by around 100,000 every month.
This week marks the third strike by specialists and the sixth by junior doctors.
NHS medical director Professor Sir Stephen Powis said: “Almost all planned treatment will be stopped and hundreds of thousands of appointments will be postponed.”
On October 2nd, 3rd and 4th, both doctoral degrees will go on strike together again.