Tens of thousands of junior doctors have gone on strike across England, with the NHS bracing itself for three days of mass disruption.
The 72-hour walkout, which began this morning, will see operations and appointments cancelled for thousands of patients.
More than 100,000 appointments have already been postponed this winter after nurses took strike action in a dispute with the government over pay, according to NHS figures.
The British Medical Association (BMA) is demanding a substantial pay rise for doctors, with its latest campaign saying junior medics could earn more per hour if they worked in Pret A Manger.
The BMA says junior doctors' pay has fallen 26% since 2008/09 and has asked the government for pay restoration.
On Friday, Health Secretary Steve Barclay invited the BMA to talks but the union rejected the idea, saying there were "unacceptable" preconditions and there had been "radio silence" from the government for months.
The preconditions are understood to have included looking at a non-consolidated lump sum payment for last year.
Junior doctors make up around 45% of the NHS's medical workforce and consultants and other medics have been drafted in to provide strike cover in areas such as A&E.
Professor Stephen Powis, medical director of NHS England, told Times Radio the health service will see "extensive disruption" over the next three days.
He said: "This is likely to be the most disruptive set of industrial action days that we've seen all winter.
"Why is that? Well, it's three days rather than just one day, it involves junior doctors that are a large part of the medical workforce and, of course, work in many healthcare settings, not just hospitals - general practice, mental health trusts and, of course, community settings too - and so it's likely that we will see that extensive disruption.
"We've been focusing on ensuring that emergency care, A&E departments, critical care, maternity services are maintained, but that's going to come, unfortunately, at the expense of other services, such as routine appointments and some surgery."
Prof Powis said cancer care is likely to affected by the strikes, saying the NHS is doing "everything we can to ensure that urgent cancer procedures go ahead but, unfortunately, even some of those may be affected this week, such is the extent of the disruption that we're likely to see".
"If that does occur, we will reschedule people as quickly as possible," he added.
Prime Minister Rishi Sunak told reporters on his flight to the US yesterday it is "very disappointing that the junior doctors' union are not engaging with the government".
It comes as members of several trade unions will strike on budget day on Wednesday in what will be one of the biggest single days of industrial action for years.
