Junior doctors have launched a five-day strike in what is being described as the longest walkout of its kind in the NHS's history amid ongoing protests over pay in the health service.
Members of the British Medical Association (BMA) in England mounted picket lines outside hospitals from 7am at the start of the walkout, which will cause huge disruption, affecting operations and consultations.
Hospital consultants and radiographers will take industrial action later this month.
The strikes are being held amid speculation the Government will say if it is going to accept recommendations from pay review bodies affecting public sector workers including teachers, civil servants and NHS workers.
There is speculation that the bodies have recommended rises of between 6% and 6.5%.
There will be renewed anger from unions if the Government rejects the recommendations or says money will have to be found from existing budgets.
BMA leaders urged the Government to return to the negotiating table in a bid to resolve the long-running row, which has already led to a series of strikes and thousands of cancelled operations and consultations.
BMA leaders Dr Robert Laurenson and Dr Vivek Trivedi said: "Today marks the start of the longest single walkout by doctors in the NHS's history, but this is still not a record that needs to go into the history books.
"We can call this strike off today if the UK Government will simply follow the example of the government in Scotland and drop their nonsensical precondition of not talking whilst strikes are announced and produce an offer which is credible to the doctors they are speaking with.
"The pay offer on the table to junior doctors in Scotland and how it was reached throws into sharp relief the obstinate approach being taken by the Prime Minister and the Health Secretary, Steve Barclay.
"The Health Secretary has said there can be no talks while strikes are planned - Scotland has proved him wrong. He said above 5% wasn't realistic - Scotland proved him wrong. He refused to even acknowledge the concept of pay restoration - Scotland proved this is not only possible but essential."
The BMA leaders said talks have to be resumed, adding: "The Government's refusal to talk with junior doctors in England who have strikes planned is out of keeping with all norms of industrial action.
"Doctors have a right to expect that as in Scotland, and as in many other recent industrial disputes, talks will continue right up to the last minute to try and reach a deal without the need to strike.
"The complete inflexibility we see from the UK Government today is baffling, frustrating and ultimately destructive for everyone who wants waiting lists to go down and NHS staffing numbers to go up.
"The Government has missed chance after chance to provide a credible offer and potentially bring to an end the industrial action by junior doctors in England and whilst there are differences between junior doctors and governments in England and Scotland, the UK Government has far more financial freedom to give doctors what they deserve."
NHS Providers has urged both sides to resume talks in a bid to head off more industrial action.
Deputy chief executive Saffron Cordery said: "The impact of these disputes is fraying the fabric of the NHS, held together by a unique sense of commitment and shared endeavour across the workforce that has served it so well over so many years. We lose that at our peril.
"The disruption for many thousands of patients and the potential harm of delaying their treatment is a huge and growing risk for the NHS to manage.
"Trusts will hardly have time to draw breath after a five-day walkout by junior doctors before consultants strike for two days, followed by a two-day strike by radiographers.
"The domino effect of repeated waves of industrial action is eroding the fundamental relationship between trust leaders and their staff.
"Trust leaders understand the strength of feeling among striking staff, who they value and work with for patients every day, and why they are taking action. Trusts will continue to do everything they can to limit disruption and keep patients safe but that's getting harder and more expensive with every strike as the cost of hiring cover grows, and with staff dissatisfaction increasing as disputes remain unresolved.
"Eight consecutive months of industrial action across the NHS are taking their toll not just on patients, with more than 651,000 routine procedures and appointments forced to be rescheduled, but on already overstretched services - hampering efforts to cut waiting lists."
Health and Social Care Secretary Steve Barclay said: "It is disappointing that the BMA is going ahead with further strike action. This five-day walkout by junior doctors will have an impact on thousands of patients, put patient safety at risk and hamper efforts to cut NHS waiting lists.
"We were in discussions about pay and a range of other measures to improve the working lives of junior doctors until their representatives collapsed the negotiations by announcing further strikes. A pay demand of 35% or more is unreasonable and risks fuelling inflation, which makes everyone poorer.
"Earlier this week I held a round table with doctors in training to talk about other key issues that affect them so we can work together to make the NHS a better place for all. We recently published the first ever NHS Long Term Workforce Plan which includes measures to better support staff, improve training and double the number of medical school places by 2031.
"If the BMA shows willingness to move significantly from their current pay demands and cancels these damaging and disruptive strikes, we can get around the table to find a fair deal to resolve this dispute."
- Polling by YouGov showed public support for strikes has remained consistent since the beginning of the year.
Nurses have the strongest public backing, with three in five Britons supporting them and three in 10 opposed.
Ambulance workers have similar levels of support, with 58% in favour and 33% opposed.